In this paper, a novel semi-fragile authentication scheme based on block-mean quantization in the wavelet domain is proposed for image authentication. The scheme is composed of a structural digital signature process and a semi-fragile watermarking/ fingerprinting algorithm. In the signature process, the invariants are extracted as authentication codes from the quantization relationships and hierarchy information of discrete wavelet decomposition. The authentication codes consist of inter-block and intrablock codes in order to detect and localize tampering. The semi-fragile fingerprinting algorithm is intended to embed the signature via the use of block-mean quantization. The proposed scheme can effectively detect and localize the malicious modification while tolerating lossy compression.