This is a montage spread for the "City at War" arc by Peter Laird:
Frankly, I'm not sure where this art came from; if it was ever published as a poster or what. I'm... not even sure how I got the thing. My "random TMNT image" folder is full of stuff that apparently substantiated out of thin air.
Regardless of origin, it's pretty sweet, isn't it?
EDIT: Aha! Thank you, Google Image Upload And Search. Peter Laird posted it on his blog some while back. Apparently it was never used for anything.
EDIT AGAIN: Looks like it finally saw life as a variant cover for TMNT: The Secret History of the Foot Clan #1 by IDW publishing.