Efficient Image Hashing with Geometric Invariant Vector Distance for Copy Detection

Hashing method is an efficient technique of multimedia security for content protection. It maps an image into a content-based compact code for denoting the image itself. While most existing algorithms focus on improving the classification between robustness and discrimination, little attention has been paid to geometric invariance under normal digital operations, and therefore results in quite fragile to geometric distortion when applied in image copy detection. In this article, a novel effective image hashing method is proposed based on geometric invariant vector distance in both spatial domain and frequency domain. First, the image is preprocessed by some joint operations to extract robust features. Then, the preprocessed image is randomly divided into several overlapping blocks under a secret key, and two different feature matrices are separately obtained in the spatial domain and frequency domain through invariant moment and low frequency discrete cosine transform coefficients. Furthermore, the invariant distances between vectors in feature matrices are calculated and quantified to form a compact hash code. We conduct various experiments to demonstrate that the proposed hashing not only reaches good classification between robustness and discrimination, but also resists most geometric distortion in image copy detection. In addition, both receiver operating characteristics curve comparisons and mean average precision in copy detection clearly illustrate that the proposed hashing method outperforms state-of-the-art algorithms.