Image authentication is applied to protect the integrity of the digital image. Conventional image authentication mechanisms, however, are unfit for the palette-based color images. Palette-based color images such as GIF images are commonly used for media communications. This article proposes a palette-based color image authentication mechanism. This novel scheme can guarantee the essentials of general authentication schemes to protect palette-based color images. Morphological operations are adopted to draw out the tampered area precisely. According to the experimental results, the images embedded with the authentication data still can preserve high image quality; specifically, the new scheme is highly sensitive to altered areas.

This paper describes a semi-fragile watermarking scheme for image authentication and tamper-proofing. Each watermark bit is duplicated and randomly embedded in the original image in the discrete wavelet domain by modifying the corresponding image coefficients through quantization. The modifications are made so that they have little effect on the image and that the watermarking is robust against tampering. The watermark image for authentication is reconstructed by taking a weighted vote on the extracted bits. The bits that lose the vote are treated as having been tampered with, and the locations of the lost bits as indicating tampered positions. Thus, authentication and tamper-proofing can be done by observing the images of watermarks that win and lose votes. Sieving, emphasis, and weighted vote were found to be effectively make the authentication and tamper detection more accurate. The proposed scheme is robust against JPEG compression or acceptable modifications, but sensitive to malicious attacks such as cutting and pasting.