A Novel Authentication Scheme for Lossy Compressed Images

In this paper, a novel scheme is proposed for watermarking lossy compressed images just before transmission and authenticating them once they are received, away from the core of the compression and de-compression processes. The scheme is inserted into the Joint Photographic Expert Group (JPEG) structure that is encoded using the Discrete Cosine Transform (DCT) at specified locations. The watermark information is extracted from and embedded into specified DCT coefficients, following novel criteria. The scheme is robust to lossy compression; though it is fragile, exposing any slight changes of the probe images. The scheme is also blind, needs no prior information about the original image or the watermark information to authenticate the received image. Experimentally, if the received watermarked data is not manipulated, the proposed scheme verifies them as 'authenticated'. On the other side, if geometrical or image processing attacks are applied to the watermarked images, they are then verified successfully as 'not authenticated'. The proposed scheme is further evaluated and compared to similar authentication schemes. The noise added to the original image due to embedding the watermark information is 0.063 dB (decibel), overcoming all results in the reviewed literature.