1. Field of the Invention
This invention relates generally to computer systems, and more particularly provides a system and method for digitally marking a file with a removable mark.
2. Description of the Background Art
Real world data, such as audio and video data, are recorded on various mediums. Older technology, such as analog audio and video tapes, analog photographs, television and radio signals, etc., record real world data in analog form. Analog data on an analog medium is difficult to modify undetectably.
However, modern systems use digital technology. Examples of such systems include digital audio recordings on tape or CD's or computer memory or hard disks, digital still or motion pictures on tape or DVD's or in computer memory or hard disks, digital still or motion pictures or digital audio data sent over the phone lines or on computer networks, digital audio signals sent over the radio waves in devices such as digital microphones or cordless telephones. Because of the ease of data manipulation of a digital file, it is difficult to detect whether recorded digital data is the original real world data or a modified version.
Some prior digital imaging systems add a “digital watermark” to an image A user typically selects a region in the image in which to replace the original real world data with a word or symbol. The digital watermark is designed to survive many types of digital editing and alteration. However, the digital watermark irrecoverably sacrifices some of the real world data and merely provides evidence of the origin of the digital work. Further, one hoping to authenticate the contents of the image cannot reasonably assume by locating the watermark in the image that the image contains only the original real world data.
Other prior digital systems append code to the real world data file containing the real world data. However, each system uses a different protocol and format. Thus, when converting a digital file between formats, the appended code is typically discarded as unnecessary. A user can thus modify the contents of the data file undetectably.
Further, compression is a technique used to reduce memory and processor power requisites. When an image is compressed using a form of lossy compression, the image content will be modified.
Therefore, a system and method are needed for encoding into a digital file a mark, which may not irrecoverably sacrifice any of the original data, which may not be lost by converting the file data between different protocols and formats, which my identify the original content, and/or which may survive lossy compression.