Abstract: In this paper, a secure and incidental distortion tolerant signature method for image authentication is proposed. The generation of authentication signature is based on Hotelling's T-square Statistic (HTS) via Principal Component Analysis (PCA) of block DCT coefficients. HTS values of all blocks construct a unique and stable ``block-edge image'', i.e., Structural and Statistical Signature (SSS). The characteristic of SSS is that it is short, and can tolerate content-preserving manipulations while keeping sensitive to content-changing attacks, and locate tampering easily. During signature matching, the Fisher criterion is used to obtain optimal threshold for automatically and universally distinguishing incidental manipulations from malicious attacks. Moreover, the security of SSS is achieved by encryption of the DCT coefficients with chaotic sequences before PCA. Experiments show that the novel method is effective for authentication.