I have my doubts too, but look at where the sun is hitting that man's face. It is on his left side of his face. Since it was morning when the attacks took place, that means that to his back is North. The first plane did come into the North tower from the north side of the building. We also know from the images and footage, the smoke from the wreakages are blowing SouthEast. The wind was coming from the NorthWest. If you also look at the skyline of NY in the background, it would go along the lines that this was taking from the North side of the North tower where the first plane did hit.
I know that it is hard to believe finding this pic, and I too are skeptic about it authenticity.
What are the fact to prove and to disprove the authenticity of this picture?
I'll look at some more footage, and see if I can compare up some more landmarks.