The ease by which digital information can be duplicated and distributed has led to the need for effective copyright protection tools. Various techniques including watermarking have been introduced in attempt to address these growing concerns. Most watermarking algorithms call for a piece of information to be hidden directly in media content, in such a way that it is imperceptible to a human observer, but detectable by a computer. This paper presents an improved cryptographic watermark method based on Hwang and Naor-Shamir [1, 2] approaches. The technique does not require that the watermark pattern to be embedded in to the original digital image. Verification information is generated and used to validate the ownership of the image or a group of images. The watermark pattern can be any bitmap image. Experimental results show that the proposed method can recover the watermark pattern from the marked image (or group of images) even if major changes are reflected on the original digital image or any member of the image group such as rotation, scaling and distortion.