Hybrid attention network with appraiser-guided loss for counterfeit luxury handbag detection

Recently, convolutional neural networks have shown good performance in many counterfeit detection tasks. However, accurate counterfeit detection is still challenging due to the following three issues: (1) fine-grained classification, (2) class imbalance, and (3) high imitation samples. To address these issues, we propose a hybrid attention network (HANet) for counterfeit luxury handbag detection. In HANet, a hybrid attention module is first designed. Compared with existing methods that directly use classic CNNs for counterfeit detection, the HA module jointly uses a channel attention unit and a spatial attention unit to learn important information on both the channel and spatial dimensions. The HA modules can be easily integrated into the ResNet architecture to enhance the discriminative representation ability of CNNs, so as to help the network find subtle differences between the real and counterfeit products. In addition, an appraiser-guided loss is proposed to train HANet. Considering the factor of class imbalance and high imitation samples, the proposed loss gives the counterfeit class a higher weighting, and meanwhile gives the high imitation samples a much higher weighting. The proposed loss introduces the knowledge of appraisers, which allows HANet to not only treat real and counterfeit samples relatively fairly, but also pay more attention to the learning of difficult samples. To evaluate the performance of our method, we have constructed a well-benchmarked luxury handbag dataset. On this dataset, the performance of HANet, ResNet50, and the state-of-the-art attention methods is compared. The results demonstrate that HANet achieve superior performance against all its competitors.


Introduction
Counterfeit goods are a massive worldwide problem, which directly affects almost all high-value products [1,2]. According to a report by the Organization for Economic Cooperation B Chengzhang Zhu chzhzhu@csu.edu.cn 1 and Development (OECD) [3], illegal trafficking of counterfeit goods accounted for 3.3% of the world trade in 2016, which was approximately $509 billion, up from 2.5% in 2013. Moreover, these figures are only based on 2016 customs seizure data, and do not include counterfeit products produced and consumed in various countries, or pirated products distributed through the Internet. At present, counterfeit goods have appeared in many industries, ranging from luxury handbags, perfume, and machine components to chemical products [4][5][6]. More seriously, some counterfeit goods even threaten the safety of human life, such as counterfeit auto parts, medical equipment with incorrect parameters, counterfeit tablets, counterfeit baby milk powder, etc. [7][8][9]. Moreover, counterfeit goods also seriously affect social security. As we all know, the profits made by counterfeiters in various markets have become one of the important sources of funds for illegal and potentially harmful activities around the world [10].
Fighting against counterfeit goods is a protracted and never-ending struggle. So far, many methods based on overt and covert technologies have been proposed for counterfeit detection [11][12][13][14][15][16]. The commonly used overt anti-counterfeiting technologies include holograms [17], bar codes, watermarks, color-changing inks, and sequential product numbers. This type of method relies heavily on the verification details that exist on the object surface, and these details can easily be reverse-engineered or removed by counterfeiters. Covert anti-counterfeiting technologies include security inks, digital watermarks, biological, chemical or microscopic taggants [18], QR or RFID tags, etc. The covert methods are usually more accurate than the explicit methods and can provide a stronger guarantee of authenticity. However, these solutions are often costly and even difficult to be adopted by commodity manufacturers. In many markets for high-value goods, manufacturers may oppose adding implicit solutions to goods, especially luxury goods, fashion, or art.
Recently, with the rapid improvement of the computing ability of GPU devices, convolutional neural networks (CNNs), as a typical algorithm in the field of deep learning, have shown extremely powerful performance in various image analysis tasks [19][20][21]. For example, in the famous ImageNet image classification competition, the recognition ability of CNNs has surpassed that of humans [19]. In the field of medical image analysis, the diagnosis performance of deep models trained by CNNs is superior to that of professional physicians [22][23][24]. Inspired by these successful practices, some studies have begun to apply CNNs for the detection of counterfeit goods. Among these methods, their main research objects are counterfeit currencies [25,26], counterfeit medicines [27,28], and counterfeit luxury handbags [29,30]. By collecting a large number of specific product images and annotating their labels (i.e., real or counterfeit), existing CNN-based methods tend to directly use CNNs to learn the difference between the real and counterfeit classes and thereby realizing the detection of counterfeit products.
Although these CNN-based methods have achieved good performance in some specific counterfeit detection tasks, their performance is still limited due to the following three issues: (1) fine-grained classification: real and counterfeit products are sometimes very similar in image appearance, and CNNs used for natural scene image classification usually lack the ability to capture these extremely subtle differences; (2) class imbalance: the number of real product images is far more than counterfeit ones; (3) high imitation products: they are difficult samples in the CNN training process, which may mislead the feature learning process and deteriorate the final counterfeit detection performance.
To solve the above problems, we propose a hybrid attention network (named HANet) with appraiser-guided loss for luxury handbag detection. Compared with existing methods that directly use classic CNNs for counterfeit detection, we propose a novel hybrid attention module, called HA module. The HA module jointly uses a channel attention unit and a spatial attention unit to learn important information on the channel and spatial dimensions, which can enable CNNs to automatically locate the discriminative regions of real and counterfeit products. In addition, an appraiser-guided loss is proposed to train HANet. Considering the factor of class imbalance, the proposed loss gives the counterfeit class a higher weighting based on the ratio of class distribution. Then, for counterfeit samples belonging to high imitations, the proposed loss further increases the weight of them. The reason why the proposed loss is called the appraiser-guided loss is that the specific determination of whether a certain counterfeit sample is a high imitation product is made by the discussion of multiple experts. With the proposed appraiserguided loss, HANet could treat real and counterfeit samples relatively fairly during the training process, and meanwhile pay more attention to the learning of difficult samples (i.e., high imitation products).
The main contributions of this paper are summarized as follows: • A novel HA module is proposed to learn important information on both channel and spatial dimensions, which can make CNNs focus more on the discriminative regions of real and counterfeit products. To the best of our knowledge, this is the first attempt to apply the attention mechanism in CNNs for counterfeit detection. • A new loss is proposed to train a counterfeit detection model under the condition of class imbalance and high imitation products. The proposed loss incorporates the expert knowledge of appraisers and gives a higher weighting to high imitations samples, thus promoting the model's learning of difficult samples during the training process. • A large luxury handbag dataset has been collected and well annotated, including four brands (i.e., Chanel, Gucci, Louis Vuitton, and Prada) and 74,916 images. On the constructed dataset, the effectiveness of HANet is demonstrated by comparing with ResNet and state-ofthe-art attention methods.

Counterfeit detection based on CNNs
Due to their powerful end-to-end feature learning capabilities, CNNs have been widely used for counterfeit detection.
In these studies, most of them study counterfeit currencies [25,26,[31][32][33] or medicines [27,28,[34][35][36], and a few investigate counterfeit luxury handbags [29,30]. For example, Desai et al. [31] proposed a method combining CNN and Regarding the detection of counterfeit luxury bags, there are only two related published studies. The first study was proposed by Sharma et al. [29]. They used two classifiers (SVM and an 8-layer CNN) to detect the authenticity of a variety of physical objects, including 20 types of leather, 120 types of fabrics, 10 types of paper, 10 types of plastic surfaces, 2 authentic NFL jerseys, and 2 types of Viagra pills. The experimental results show that the recognition performance of CNN is higher than that of SVM. In addition, they stated that their method has been deployed to verify the authenticity of luxury handbags. An obvious limitation of this method is the requirement of a special imaging equipment to display the details of products, which is often unfriendly to the end users. Target at this problem, Serban et al. [30] proposed a more friendly counterfeit detection system for luxury handbags. This system developed multiple CNN models (i.e., VGG-16 models) to detect the authenticity of different parts of the handbag. Regarding the counterfeit detection of Louis Vuitton (LV) handbags, the counterfeit detection parts include buckles, etiquettes, and textures. In its actual use stage, this system requires users to upload the specified part image according to the prompt, and then applies the corresponding CNN model to test its authenticity score.
In summary, existing CNN-based methods for counterfeit detection mainly focus on the studies of counterfeit currencies and medicines. In the few published papers that support counterfeit luxury handbag detection, they only verified the performance of their methods on a limited dataset, such as some physical objects and LV handbags. As a result, the performance of their methods on multiple brands of luxury handbags is not sure. In addition, their methods are simple CNN models, such as 8-layer CNN or VGG-16. Due to the limited feature representation capabilities, their performance on some complex counterfeit detection tasks may be challenged.

Image classification based on attention mechanism
The attention mechanism in deep learning is similar to the attention mechanism of human vision, i.e., selecting key points from a large amount of information while ignoring other irrelevant information. It has brought many breakthroughs in the fields of natural language processing [37,38] and computer vision [39,40]. Recently, the attention mechanism has also been used to improve the feature representation ability of CNNs in large-scale image classification tasks [41,42]. For example, Wang et al. [41] proposed a residual attention network called RAN, which is stacked by multiple attention modules in the residual network. Each attention module consists of a trunk branch and a mask branch, where the trunk branch is used for feature processing, and the mask branch employs an encoding-decoding structure to learn the corresponding attention feature map. Hu et al. [42] proposed a new attention-based network called SENet, which consists of a series of squeeze and excitation (SE) blocks. The SE block explicitly uses two fully connected (FC) layers to learn the importance of each channel, where the first FC layer compresses the original feature map in the channel dimension and the second FC layer restores the number of channels to the original size.
Because the attention mechanism has the characteristics of helping the network locate the discriminative and meaningful regions on the image, it has also been applied to fine-grained image classification tasks [43][44][45][46]. For example, Zheng et al. [43] proposed a part learning method based on multi-attention CNNs for fine-grained classification, in which part generation and feature learning can reinforce each other. Peng et al. [44] proposed an object-partial attention model for weakly supervised fine-grained image classification, in which the object-level attention locates the object of the image, and the partial-level attention selects the discriminative part of the object. Zhang et al. [45] proposed a residual attention network for skin lesion classification, which contains an attention residual module that combines residual learning and spatial attention mechanisms. Huynh et al. [46] proposed an attention mechanism based on dense attributes for fine-grained classification of small samples. This mechanism can focus on the most relevant image regions for each attribute and obtain attribute-based features accordingly.
Although the attention mechanism has many successful applications in the field of fine-grained image classification, its performance has not yet been verified in counterfeit detection tasks. As described in "Introduction", counterfeit detection tasks belong to the fine-grained classification. Therefore, to further boost the performance of the counterfeit detection, it is necessary to incorporate the attention mechanism into the counterfeit detection method.

Fig. 1 Overview of the proposed HANet
Proposed approach Overview Figure 1 shows the overall framework of HANet. The input of HANet is a part image of a luxury handbag, and the output is the counterfeit detection prediction of this image. Specifically, HANet includes a convolutional layer, a max pooling layer, a series of the combination of residual blocks and the hybrid attention (HA) modules, a global average pooling layer, and a fully connected layer. Overall, HANet adopts the macro-structure of ResNet, i.e., adopting the skip connections and residual learning mechanism. Therefore, similar to ResNet, HANet could also be stacked deeply while avoiding the vanishing gradient problem. Different from ResNet, HANet uses the attention mechanism to learn important information on both channel and spatial dimensions to optimize the features at different stages, with the aim of improving the discriminative representation ability of the network. Specifically, the HA module is inserted after the residual blocks of each stage of the network. It optimizes the output features of the current stage's residual block and sends the optimized features to the next stage to continue feature extraction. In addition, considering the issues of class imbalance and high imitation samples, a new loss that incorporates the knowledge of appraisers is proposed to train HANet. The details of the HA module and the loss are introduced in the following.

HA module
As discussed in "Introduction", since counterfeit detection is a fine-grained classification task, existing CNN-based methods may be difficult to capture the differences between real and counterfeit classes, thereby leading to limited recognition performance. To this end, we designed an HA module with a hybrid attention mechanism to explore important information on channel and spatial dimensions, aiming at enhancing the discriminative representation capabilities of the network and achieving more accurate counterfeit detection.
The specific structure of the HA module is shown in Fig. 2. Its input is the feature map output by the residual blocks, denoted as F ∈ R C×H ×W (C, H , and W represent the channel number, height, and width of the feature, respectively). First, a 1 × 1 regular convolution is performed on F to generate F c ∈ R C×H ×W and F s ∈ R C×H ×W , respectively. Subsequently, F c and F s are processed by a channel attention unit and a spatial attention unit, respectively. These two attention units are introduced in the following.
For the channel attention unit, the input feature map F c is processed by a global max pooling (GMP) layer and a global average pooling (GAP) layer on the spatial dimension to obtain two C × 1 × 1 feature maps. Then, they are, respectively, sent to a multi-layer perceptron (MLP) composed of two 1 × 1 convolutional layers. In the MLP, the number of output channels of the first convolutional layer is C/r (r is the reduction rate which is set to 16 in this paper), and the number of output channels of the second convolutional layer is C. Then, the two feature maps output by the MLP are fused by an element-wise addition. Then, a sigmoid activation operation is performed to generate the channel-wise attention weight, denoted as W c ∈ R C×1×1 . Finally, W c and F c are element-wise multiplied to generate the channel-wise attention feature map A c . The operations of the entire channel attention unit can be summarized as the following two formulas: where GMP s (·) and GAP s (·) represent global average and global max pooling operations on the spatial dimension, respectively, w m0 and w m1 represent two 1 × 1 convolutions following the GMP layer, w a0 and w a1 represent two 1 × 1 convolutions following the GAP layer, σ (·) represents the Regarding the spatial attention unit, the input feature map F s is processed by a GMP layer and a GAP layer on the channel dimension to obtain two 1 × H × W feature maps. Subsequently, the two feature maps are concatenated on the channel dimension, and the number of channels is reduced to 1 via a 1 × 1 convolution. Then, a sigmoid function is performed on this single-channel feature map to generate the spatial-wise attention weight, denoted as W s ∈ R 1×H ×W . Finally, the spatial-wise attention feature map A s is generated through the element-wise multiplication of W s and F s . The operation of the entire channel attention unit can be summarized as the following two formulas: where GMP c (·) and GAP c (·) represent global average and global max pooling operations on the channel dimension, respectively, Cat represents the feature concatenation operation on the channel dimension, and w 2 represents the 1 × 1 convolution. Finally, the output of the HA module is the weighted summation of A c , A s , and F where F re f ined represents the final refined feature map, and α and β are two learnable weighting factors to adjust the contributions of A c and A s in F refined , respectively. α and β are initially set to 0, and their values can be adaptively learned during the model training process. From the above descriptions, it can be observed that the proposed HA module jointly uses the channel and spatial attention mechanisms to learn and capture important information of the input feature map. In the literature, there are also some existing hybrid attention methods that integrate both channel and spatial attention mechanisms, such as CBAM [47] and DANet [48]. For the input feature map, CBAM first executes a channel attention module, and then applies a spatial attention module to the output feature map of the channel attention module to obtain the final refined feature map. Compared with CBAM that uses a serial channel-spatial attention structure, the HA module uses two parallel attention units to implement the channel and spatial attention mechanisms, so that the learning process of the two attention mechanisms can be decoupled. DANet has parallel position and channel attention modules, which is similar to our HA module. However, the self-attention operations in these two modules are computationally expensive, resulting in slow model training and inference speed. Compared with DANet, the proposed HA module uses GMP and GAP operations, which can greatly reduce model parameters and lower the computational complexity. Moreover, the output of the HA module not only contains the channel and spatial attention feature maps, but also includes the original input feature map. In this way, the convergence of model training can be guaranteed, and the representation ability of the network can also be enhanced.

Loss function
In the existing methods for counterfeit detection, most of them use the original cross-entropy loss for model training. However, an obvious fact is that there exists heavy class imbalance in counterfeit detection tasks, i.e., there are far more real products than counterfeit products. In addition, there also exists a certain number of high imitations that are easily confused with the real ones, which are called hard negative samples. It is well known that the problem of class imbalance will cause the model to be biased toward classes with more samples, and the difficult samples will mislead the model training process. To solve these two problems, we propose a appraiser-guided loss. The proposed loss first gives a higher weighting to the non-representative class (i.e., the counterfeit class) to alleviate the impact of class imbalance on training. Then, a much higher weighting is given to the samples annotated as high imitations to make the model focus more on these hard negative examples. Given that the number of real and counterfeit samples in the training data are M and N, respectively, the proposed appraiser-guided loss is defined as follows: where x i and y i represent an input image and its label, φ(x i ; θ) represents the predicted result with the input of x i (θ represents the parameters of the network and φ(·) represents the input to output mapping of the network), and ω(x i ) is a weighting factor function according to x i . Specifically, ω(x i ) is defined as follows: where P, N normal , and N hard represent the sets of real samples, counterfeit samples that do not belong to high imitations (i.e., general counterfeit samples), and counterfeit samples that belong to high imitations (i.e., high imitation samples). To give high imitations a greater loss weighting, k > 1. Here, we set k to 1.5 in all experiments of this paper. From Eqs. 6 and 7, we can draw the following two conclusions: (1) in the proposed loss, since M > N , the general counterfeit samples receive a higher loss weighting than the real samples; (2) since k > 1, the high imitation samples obtain a higher loss weighting than the general counterfeit samples. From the above two conclusions, the proposed appraiser-guided loss has the potential to address the issues of class imbalance and high imitations in counterfeit detection tasks.

Analysis of principle
As described before, HANet is a kind of attention-based CNN method designed for counterfeit detection. In the following, we compare HANet with existing CNN-based counterfeit detection methods and other attention methods: • For existing CNN-based counterfeit detection methods, they usually directly employ classic CNNs for classification. However, the real and fake products are sometimes very similar in image appearance, and the CNNs designed for natural scene image classification tasks may lack the ability to capture these subtle differences. To address this issue, an HA module is designed to learn important information on both channel and spatial dimensions, which can be easily integrated into the ResNet architectures and help the network locate the discriminative regions of real and counterfeit products. • Existing attention methods can be simply divided into channel, spatial, and hybrid attention methods. The first two kinds of methods learn importance on channel and spatial dimensions, respectively, while the hybrid ones aim at learning important information on both two dimensions. CBAM [47] and DANet [48] are two representatives of hybrid attention methods. As discussed in "HA Module", compared with CBAM, HANet could obtain better channel and spatial attention maps using two parallel attention units to decouple the two attention learning mechanisms. Compared with DANet that also uses two parallel attention units to implement the channel and spatial attention mechanisms, HANet has advantages in model size and computational complexity. • In addition, HANet differs from existing CNN-based counterfeit detection methods in the loss function. For most CNN-based counterfeit detection methods, they usually use the original cross-entropy loss for model training. However, their training performance may be deteriorated due to the challenges of heavy class imbalance and high imitation samples. To deal with these two challenges, an appraiser-guided loss is proposed to train HANet, which first gives the counterfeit class a higher weighting based on the ratio of class distribution and then further increases the weight of counterfeit samples belonging to high imitations. By doing so, HANet could treat real and counterfeit samples relatively fairly during the training process and pay more attention to the learning of difficult samples.

Dataset
To verify the performance of the proposed algorithm, we have collected and well-labeled a luxury handbag dataset. To collect this dataset, we have designed an online program for the verification of luxury bags. In this program, the users can upload the pictures of luxury bags that need to be authenticated according to the requirements of our program, and then, the authenticity of the uploaded pictures is verified by the appraisers from a third-party professional appraisal agency. Through this online verification program, we have  collected a large number of pictures of luxury bags, and each picture has the ground-truth label of real or counterfeit. Overall, the dataset has 74,916 high-quality luxury handbag images, covering four luxury brands. The four luxury brands are Chanel, Gucci, Louis Vuitton, and Prada, which contain 15,458, 14,697, 34,131, and 10,630 images, respectively. Some sample images of the dataset are shown in Fig. 3. In this dataset, the images are all part images of luxury handbags labeled by appraisals. The real and counterfeit labels are repeatedly confirmed by multiple appraisers. According to the general rules of luxury bag identification, there are 12 general identification parts: bag, button, coding, embossing, front, hasp, label, lock, logo, sign, tag, and zipper. Different brands of luxury handbags may have different identification parts. For example, for CHANEL, its identification parts include coding, front, hasp, sign, and tag. For GUCCI, its identification parts include bag, button, coding, front, sign, and tag. For each brand, the number of images of different parts and the number of real and counterfeit images are given in Table 1. It can be seen from the table that the number of real samples is obviously more than that of the counterfeit ones. The class imbalance makes the counterfeit detection task more difficult.

Algorithms for comparison
As mentioned earlier in 'Proposed approach', the proposed HANet is built by integrating the channel and spatial attention mechanisms into ResNet. Therefore, the algorithms used for comparison include the baseline (ResNet50 [19]) and attention methods, including SENet50 [42], RAN50 [41], ARL-CNN50 [45], and CBAM50 [47]. Among these attention methods, SENet50 belongs to the channel attention methods, RAN50 and ARL-CNN50 belong to spatial attention methods, and CBAM50 belongs to the hybrid channel and spatial attention methods. It is worth mentioning that these attention methods and the proposed HANet all use the macro-architecture of ResNet50, so the depth of the network is basically the same, which can ensure the fairness of the comparisons in our experiments. The number of parameters and computational complexity of these algorithms are shown in Table 2. We use the indicator of floating point operations (FLOPs) to represent the computational complexity of a deep learning model. Note that these two indicators are calculated on the input image with the resolution of 256 × 256 × 3. It can be seen from Table 2 that compared with the original ResNet50, the increase in the number of parameters and computational complexity of ARL-CNN50 is negligible, while that of RAN50 is the largest among these attention methods. Compared with CBAM50, which is also a hybrid attention method, HANet has relatively fewer parameters and lower computational complexity.

Implementation details
In the training phase, for each brand of the luxury handbag, we need to train an independent counterfeit detection model for each identification part. According to the conventions of machine learning, we divided the original dataset with the ratio of 3:1:1, i.e., 3/5, 1/5, and 1/5 data were used for model training, validation, and test, respectively. Next, we adjusted the image size to 256 × 256. To avoid the over-fitting problem, online data augmentations were implemented, including random rotation ([40; +40 ]), zoom (90%-110% of width and height), and horizontal and vertical flips. The SGD algorithm was adopted as the optimizer, with the momentum of 0.9, weight decay of 0.0005, and batch size of 16. The learning rate was initially set to 0.001, and halved every 50 epochs.
To speed up the training process, we loaded the pre-trained parameters on ImageNet of the original ResNet. The maximum number of training epochs was set to 300. We retained the model with the best performance on the validation set, and used the model to test on the corresponding test set to obtain the final performance.

Compared with the baseline and attention methods
First, we compared the performance of HANet with that of the baseline (ResNet50) and attention methods on the luxury handbag dataset. The experimental results of Chanel,  Table 6, it shows that HANet achieves the highest accuracy on six identification parts of Prada (button, embossing, label, sign, tag, and zipper), and the second highest accuracy on other two identification parts (front and logo). Compared with the baseline, HANet improves the accuracy by 1.9%, 2.1%, 1.5%, 1.0%, 1.1%, 1.9%, 1.8%, and 2.2% on the Prada's button, embossing, front, label, logo, sign, tag, and zipper, respectively. To summarize, the above results suggest that HANet has better performance than the baseline and attention methods on our collected luxury handbag dataset.
In particular, compared with CBAM50 that also belongs to a hybrid attention method, HANet not only achieves superior performance, but also has fewer parameters and lower computational complexity (Table 2).

Ablation study
HANet includes two main components: the HA module and the appraiser-guided loss. To investigate their effectiveness, we conducted the ablation experiments on each of them. For each identification part, the highest performance is highlighted in boldface For each identification part, the highest performance is highlighted in boldface  Tables 7 and 8 give the ablation results on Gucci and Louis Vuitton of the luxury handbag dataset, respectively. In these experiments, HANet without the HA module represents the variant obtained by deleting the HA modules in HANet (the appraiser-guided loss is retained), and HANet without the appraiser-guided loss represents the variant obtained by replacing the appraiser-guided loss with regular binary crossentropy loss.
(1) Effectiveness of the HA module: To valid the effectiveness of the HA module, we compared the results of HANet and HANet without the HA module. From Table 7, it suggests that the application of the HA module improves the accuracy by 1.6%, 1.4%, 1.3%, 1.6%, 1.4%, and 1.7% on Gucci's bag, button, coding, front, sign, and tag, respectively. From Table 8, it indicates that the usage of the HA module improves the accuracy by 1.4%, 1.3%, 1.0%, 1.0%, 1.6%, and 1.3% on Louis Vuitton's button, coding, front, lock, sign, and zipper, respectively. In summary, the above results demonstrate the effectiveness of the HA module in HANet.
(2) Effectiveness of the appraiser-guided loss: We also compared the results of HANet and HANet without the appraiser-guided loss. From Table 7, the employment of the appraiser-guided loss improves the accuracy by 0.5%, 0.3%, 0.4%, 0.4%, 0.3%, and 0.4% on Gucci's bag, button, coding, front, sign, and tag, respectively. From Table 8, it shows that the usage of the appraiser-guided loss improves the accuracy by 0.2%, 0.3%, 0.1%, 0.1%, 0.4%, and 0.3% on Louis Vuitton's button, coding, front, lock, sign, and zipper, respectively. In summary, the above results demonstrate the effectiveness of the appraiser-guided loss in HANet.

Conclusion
In this paper, we proposed HANet for counterfeit detection in luxury handbag images. In HANet, an HA module with a hybrid attention mechanism was first designed. Compared with existing methods that directly use classic CNNs for counterfeit detection, the HA module jointly uses a channel attention unit and a spatial attention unit to learn important information on both the channel and spatial dimensions. The proposed HA module can be easily integrated into the For each identification part, the highest performance is highlighted in boldface ResNet architecture to help the network find subtle differences between the real and counterfeit products. In addition, an appraiser-guided loss was proposed to train HANet. Considering the factors of class imbalance and high imitation samples, the proposed loss gives the counterfeit class a higher weighting and gives the high imitation samples a much higher weighting. The proposed loss introduces the knowledge of appraisers, which allows HANet to not only treat real and counterfeit samples relatively fairly, but also pay more attention to the learning of difficult samples. We evaluated the performance of HANet on our self-constructed dataset, a large and well-benchmarked luxury handbag dataset. The results showed that HANet could achieve superior performance against the state-of-the-art methods.
In the future, we plan to design a more effective attention module to further improve the performance of counterfeit detection. Moreover, we also intend to collect as more data as we can to verify the generalization performance of our model.