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Certified Defense for Content Based Image Retrieval
This paper develops a certified defense for deep neural network (DNN) based content based image retrieval (CBIR) against adversarial examples (AXs). Previous works put their effort into certified defense for classification to improve certified robustness, which guarantees that no AX to cause misclassification exists around the sample. Such certified defense, however, could not be applied to CBIR directly because the goals of adversarial attack against classification and CBIR are completely different. To develop the certified defense for CBIR, we first define new certified robustness of CBIR, which guarantees that no AX that changes the ranking of CBIR exists around the query or candidate images. Then, we propose computationally tractable verification algorithms that verify whether the certified robustness of CBIR is achieved by utilizing upper and lower bounds of distances between feature representations of perturbed and non-perturbed images. Finally, we propose new objective functions for training feature extraction DNNs that increases the number of inputs that satisfy the certified robustness of CBIR by tightening the upper and lower bounds. Experimental results show that our objective functions significantly improve the certified robustness of CBIR than existing methods.