A watermarking scheme is provided that allows the watermarked image to be authenticated by an authentication agent without revealing the human-readable content of the image. There is disclosed an approach that combines privacy control with watermarking and authentication mechanisms. The watermark can be made to be imperceptible to humans. Public key cryptography allows the authentication agent to authenticate without being able to watermark an image. Watermark information may also be encoded in a vector graphics image that includes at least one stroke defined by coordinate values of an ordered sequence of points. This may be obtained by providing watermark information as a bit sequence, identifying one or more redundant properties of the image, modifying the redundant properties based upon the bit sequence to generate a representation of the image and storing the representation of the image for subsequent use.