In this paper we propose a new method for invisibly watermarking high-quality color and gray-scale images. This method is intended for use in image verification applications to determine whether the content of an image has been altered, due perhaps, to the act of a malicious party. It consists of both a watermarking process which stamps a watermark into a source image without visual degradation, and a watermark extraction process which extracts a watermark from a stamped image. The extracted watermark can be compared with the embedded watermark to determine whether the image has been altered. The processing used in the watermarking and watermark extraction processes will be presented in this paper. In addition, we shall describe some modifications that provide better security, and an adaptation of the scheme to watermark JPEG images. Experimental results are reported. Some advantages of this technique over other invisible watermarking techniques for verification will be discussed; these include a high degree of invisibility, color preservation, ease of extraction, and a high degree of protection against the retention of a correct watermark after alteration by a malicious party.