This document describes the changes made to the software between the previous and current versions (see above). If you don't find something listed here, then it was not done in this timeframe, or it was not considered important enough to be mentioned. The following information is located here:
The ChangeLog will follow, but please note the most important change: LZW compression has been removed.
Unisys has the patent on LZW compression and have been very active in their enforcement of late, demanding payments of $5000 or more from websites using unlicensed software to create GIF's. They could well do the same do persons using libtiff to create LZW compressed TIFF images.
From Burn All GIF's Day:
The catch is that it appears to be difficult or impossible to get a Unisys license to use LZW in free software that complies with the Open Source Definition
Unfortunatly, the removal of LZW compression means that saved image size has grown dramatically. Without a change in the TIFF spec to support another lossless compression format, this is unavoidable.
The library can use zip for lossless compression, but as this is not part of the spec, TIFFs using zip compression may not work with other software
We will be making a patch available that will contain the LZW compression code for users who have either obtained a license from Unisys or are willing to risk it.
LZW decompression is unchanged.