GIF was fully open and free, before it wasn't. After it had established itself as a standard, was when Unisys and IBM started in with the patent they had on th

GIF was fully open and free, before it wasn't. After it had established itself as a standard, was when Unisys and IBM started in with the patent they had on the compression algorithm. Note that GIF could have switched to a different compression format, but that would have had the same issue that PNG had in that new images wouldn't be compatible with existing viewers (and that was in the days before the concept of "evergreen" web browsers -- they didn't get automatic frequent updates). And the other thing holding back the switch to PNG was that people weren't all that confident that there weren't any unknown patent landmines in that standard. You don't know until either one goes off (some patent troll convinces a court that a generically worded patent applies), or until enough time elapses (20 years) that all potential patents would have expired.