The Unisys patent on the LZW (Lempel—Ziv—Welch) compression used in *.gif ran out 2003-06-20 in the USA. It dragged on longer in other countries. The counterpart patents in the United Kingdom, France, Germany and Italy expired on 2004-06-18, the Japanese counterpart patents expired on 2004-06-20 and the counterpart Canadian patent expired on 2004-07-07. Consequently, while Unisys has further patents and patent applications relating to improvements to the LZW technique, the *.gif format may now be used freely.
You may display uncompressed *.gif files without restriction, and you can even make them for commercial purposes without restriction. What in former times you could not do is make commercial compressed *.gif files without directly or indirectly paying a royalty. What keeps *.gif files alive (even though *.png format is superior in every way) is a feature that Netscape added to them — animation. Animated *.gifs contain several images that are displayed in rotation to create a simple repetitive animation. Starting in JDK (Java Development Kit) 1.6 Java has support for animated *.gifs. Prior to that, you had to take the *.gifs apart yourself and animate them manually.
The format of the *.gif file header is as follows:
|version||87a or 89a||3 bytes|
|width in pixels||2 bytes unsigned binary little endian|
|height in pixels||2 bytes unsigned binary little endian|
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