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The GIF image format is widely used on the World Wide Web. To make a GIF image, the LZW algorithm is required. Until 2004, this algorithm had problems with patents that were aggressively enforced.

After this format became widely used, a company called Unisys began threatening developers and distributors with patent infringement based on a 1983 patent, US-4,464,650. (patent ambush)

As of 2004, that patent is expired and GIF is generally considered to be free of patent problems.

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