Why is this a change I'd want to change back, you say? While I like .jpg for compression, I will be the first to admit it's not the format I normally think of as being the best for graphic quality as someone who works with images a lot. That said, for all of you graphic fiends out there like me -- makers of icons, wallpapers, and various other graphic goodies -- here is an important imaging tip for you from your friends at the EU WoW Forums:
As of 2.1.0 WoW will now automatically save your screen shots as .jpg, i.e. JPG format. This will cut down size immensely, but it will also cut out some details due to JPG being a lossy format. I've heard a lot of people requesting if it's possible to change the format which screen shots are saved in, for those people who want to change the format back to TGA you'll have to do the following (when 2.1.0 is out)
/console screenshotFormat tga
/console screenshotQuality 10
You can also look for the 2 lines in config.wtf:
Change them to what you want and start the game.
Both commands are important, the screenshotQuality is set to 3, which makes it look like a JPG, but in TGA format.
So this concludes my guide on how to change to TGA when 2.1.0 hits, and if you want it back to normal you can use these commands:
/console screenshotFormat jpg
/console screenshotQuality 3
Optionally you could could create an add-on utilizing this, using SetCVar ( http://www.wowwiki.com/API_SetCVar
[via noabsolutes on the WoW LJ Community]