Abstract: Techniques are provided for establishing an association between a code and a user. Before a software product is provided to the user, the code is stored within the software product. The software product is configured to convert the code into a visual watermark, which is displayed on at least one screen image generated by the software product. Techniques are also provided for identifying a visual watermark in a screen image and decoding the visual watermark into a corresponding code. The user associated with the code can then be identified.

Abstract: An optical convergence apparatus (10, 310) having a projection screen (12) with a plurality of display areas (14) for displaying a like plurality of images (16). The images (16) are viewed by a plurality of lens assemblies (18) placed between the projection screen (12) and the user's eye (20). Prisms (322) are optionally provided between the lens assemblies (18) and the user's eye (20) for directing the images (16) to the user's eye (20). A stereoscopic pair (424) of the optical convergence apparatus (10, 310) is provided to enable stereoscopic reference cues.

Abstract: An apparatus and method of disabling an unauthorized copy of a computer program. A set of numbers having an uncommon mathematical property is defined. For authorized copies, one of these numbers is written to a pre-determined location in the computer program. Whenever a copy of the computer program is attempted to be run, the computer system is instructed by the computer program to check the number at that pre-determined location. A determination is then made as to whether that number has the uncommon mathematical property. The computer program is disabled if its number at that location does not have the uncommon mathematical property.