All GIF-related LZW compression patents had expired by 2004. GIF uses Lempel–Ziv–Welch, or LZW, to compress image data without loss, and patent restrictions on that technique shaped the format’s early history.
The key U.S. Unisys patent expired on June 20, 2003. However, related patents in several other countries, including the United Kingdom, France, Germany, Italy, Japan, and Canada, lasted into 2004. That is why 2004 is commonly given as the year when the worldwide patent problem surrounding GIF’s LZW compression was over.
The controversy began in the 1990s when Unisys sought licensing fees for commercial use of LZW. Because GIF was already widespread on the Web, the policy alarmed developers and helped motivate the creation of PNG in 1995 as a patent-unencumbered alternative.
The patents covered the compression technology, not the GIF name or every aspect of the file format. Once the relevant patents expired, developers could implement LZW-based GIF tools without those earlier patent royalties, helping remove a major barrier to continued GIF use.