Abstract: Plural-bit data is encoded in an image without leaving apparent evidence of image alteration. The image is represented by data elements (e.g., pixels) whose values are changed to effect the encoding. The particular data elements to be changed are selected not on their individual values, but rather on an attribute of a neighboring group of data elements.

Abstract: Technology is now available permitting consumers to make amateur- or even professional-grade copies of photographs. For wedding and portrait photographers, in particular, the business of making duplications is fundamental to their livelihoods. The threat of such copying is felt strongly. To redress these concerns, a machine-readable marking is provided on emulsion films, photographic papers, and the like. The marking encodes digital information, yet is essentially imperceptible to the human eye. A photographic duplication kiosk can be constructed to read this embedded information and, if warranted by the embedded information, to disable the kiosk's copying function. An exemplary embodiment pre-exposes the photographic product with a spatial domain representation of the embedded data, and may include rotationally symmetric one- or two-dimensional patterns. Numerous other implementations are similarly practical.

Abstract: Plural-bit data is encoded in an image without leaving apparent evidence of image alteration. The image is represented by data elements (e.g., pixels) whose values are changed to effect the encoding. The changes are desirably effected in groups, e.g., pixel groupings 5-10 pixels in height and width, and in a manner calculated to keep the changes relatively inconspicuous.