15 The GIF Legal Position

The Lempel-Ziv-Welsh (LZW) compression algorithm is patented by UniSys. This algorithim is used in the GIF image standard to store the image data inside the GIF image, and because of this software which creates GIFs are subject to licensing fees by UniSys. However Unisys has refused to issue licences to open-source software producers for the use of LZW.

While this contraversy has being going on for several years, Unisys recently (late 1999) raised the stakes by stating that its policy is to require a $5000 fee (so called Intranet or Billboard Web site license) from web sites, even non-commerical web sites, that carry GIF images made by unlicensed software. If you make use of GIF images on your web site that have been generated with an unlicenced piece of software you may be guilty of “contributory infringement”. Alarmingly, the LZW compression algorithim is also used in the popular PDF format. Open source software written to handle PDF files is therefore also at risk from this decision.

While it is debatable whether the patent covers LZW decompressors, while the Open Source community take the view that it does not, Unisys argues otherwise. It is possible you may be liable if you distribute code which implements LZW decompression.

For a history of the patent controversy, see http://lpf.ai.mit.edu/Patents/Gif/Gif.html and http://www.cloanto.com/users/mcb/19950127giflzw.html. To avoid legal problems, it would be a good idea to convert all GIFs on your web sites to PNGs or JPEGs.

When does all this nonsense go away? The basic U.S. patent on the LZW algorithim expires in June of 2003, however patents on variants of the basic algorithim run for another 20 years and further U.S. applications are pending.