In this paper a new patch-based digital signature (DS) is proposed. The proposed approach similar to steganography methods hides the secure message in a host image. However, it uses a patch-based key to encode/decode the data like cryptography approaches. Both the host image and key patches are randomly initialized. The proposed approach consists of encoding and decoding algorithms. The encoding algorithm converts the characters stream of the secret message to the patches stream of the DS image. The final image is further distorted by noise to hide the source patches. Nevertheless, the decoding algorithm uses a similarity measure to decode the DS image. Experimental results demonstrated that it is significantly robust against noise. The proposed approach has been successfully used for digital signature generation/verification and software copyright protection.

Keywords