the subject says it all: is it possible to take an image present in the clipboard and save it to file under Tkinter?
Well tkinter uses the PIL for most of its advanced image stuff, in which case this problem is quite simple: Just use Image.frombuffer(mode, size, data) with the bytebuffer representing the image and then save it ala im.save(filename)- if you want a special format you can also specify it.
If you want to do it without the PIL, I don't think tkinter offers that kind of functionality out of the box, its image support is extremely limited in itself.
save the image in the clipboatd - in Python/Tkinter