Today US Patent 4,558,302 expires. It is the patent for the LZW compression algorithm used in .gif files, held by Unisys. There are two main types of image files on the web - .jpg (or .jpeg) typically used for photos and .gif which is still heavily used because of it works better for graphics, can do transparency, and supports animation. There is another format, .png, which can do all that .gif can do and accomplish it much more efficiently (smaller file sizes), but the big hangup with its acceptance is that the popular web browsers of the day don't support all of .png features. Microsoft Internet Explorer, which is used by a majority of net travelers does not properly support even the transparency features of .png. The cash cow for Unisys is about empty. Though I'm not sure what the status is in other countries that uphold software patents.

I still find it incredulous that an entity could claim a trademark on an algorithm. It's like someone saying you can't use the pythagorean theorem or that pi is protected and everytime you use a practical application of a mathematical truth, you are compelled to pay a royalty to the owner of that mathematical "algorithm".