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Web bugs
Small image in an HTML page with all dimensions set to 1 pixel. Because of its insignificant size, it is not visible but used to pass certain information anonymously to thirdparty sites. Mainly used by advertisers. Can also be referred to as a Web beacon or invisible GIF.
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An overlaid image that is invisible to the naked eye, but which can be detected algorithmically. There are two different types of invisible watermarks: fragile and robust.
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A method of steganography that uses a special ink that is colorless and invisible until treated by a chemical, heat, or special light. It is sometimes referred to as sympathetic ink.
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Short for picture element, a pixel is a single point in a graphic image. It is the smallest thing that can be drawn on a computer screen. All computer graphics are made up of a grid of pixels. When these pixels are painted onto the screen, they form an image.
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An encoding algorithm that takes random pairs of pixels and brightens the brighter pixel and dulls the duller pixel and encodes one bit of information in the contrast change. This algorithm creates a unique change, and that change indicates the absence or presence of a signature.
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Web beacons are images that are placed in HTML documents (Web pages, HTML email) to facilitate user activity tracking. Web beacons are usually used in conjunction with cookies and are often used to track visitors across multiple internet domains. Web beacon images are usually, but not always, small and “invisible. ”
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