A distortion-free authentication method for color images with tampering localization and self-recovery

For immediate access and online backup, cloud storage has become a mainstream way for digital data storage and distribution. To assure images accessed or downloaded from clouds are reliable is critical to storage service providers. In this study, a new distortion-free color image authentication method based on secret sharing, data compression and image interpolation with the tampering recovery capability is proposed. The proposed method generates elaborate authentication signals which have double functions of tampering localization and image repairing. The authentication signals are subsequently converted into many shares with the use of (k, n)threshold method so as to increase the multiplicity of authentication signals for reinforcing the capability of tampering recovery. These shares are then randomly concealed in the alpha channel of the to-be-protected image that has been transformed into the PNG format containing RGBA channels. In authentication, the authentication signals computed from the alpha channel are not only used for indicating if an image block has been tampered with or not, but used as a signal to find the corresponding color in a predefined palette to recover the tampered image block. Compared with several state-of-the-art methods, the proposed method attains positive properties including losslessness, tampering localization and tampering recovery. Experimental results and discussions on security consideration and comparison with other related methods are provided to demonstrate the outperformance of the proposed method.