Pam, I heard about it the first time when I visited Snopes.com last night. Snopes is a website that debunks all the latest chain emails and urban legends making the rounds. They did not have any evidence that this was a retouched photo; in fact, on that website they had two photos from two sources.
http://www.snopes2.com/spoons/photos/wtcface.htm

I might be one of the world's most cynical skeptics. In fact, when I got that Nostradamus email making the rounds, I immediately researched it and found for myself what Snopes and others are only just now finding out - that the quatrain was not at all written by Nostradamus, but by a student a couple of years ago showing how ambiguous his "predictions" were.

But these photos are too eerie.

The thing that I still keep thinking, though, is why they are showing up three and four days later. They were blatantly obvious in these photos. As many video and still cameras as there were pointed at those towers, and as many thousands of times they were shown over and over in the first few hours of worldwide, all-channel coverage, it seems to me someone, somewhere would have noticed them in those first few hours.