Turning to .tga screenies has already been proposed (or more exactly, setting a choice system) on the Suggestion Boxcar Forum.
The real problem, I'm afraid, comes from fact that even uncompressed .jpg files ( a Nobel prize in 'something' :hehe: would go the guys of the Joint Picture Group) are lossy anyhow.
Just compare any of the T4/T10 .tga screenies with any of a .jpg converted into .tga and see the difference... apparently none but set you good old friend PeehEs to a 1000X with actual pixel view.. and you'll see.
Saving is not always the best way to go. And I mean saving HD space... :hehe: I don't want misunderstandings with any trainzy banker over here.
It's also unfortunate that the TS2010 screenshots are not in the 4x3 format of eg. TRS2004 so that they could be more easily scaled to the required 240x180.