It's pretty much a given that the five Pentagon security camera frames were dodgied up. When they were first released I stared at them until my brain ached trying to see a plane in frame 1 and I reckon many other people did too.
Then the penny dropped. We are meant to play find-the-jet otherwise the frames would never have been released. This means that a) there really is a Boeing 737 200 somewhere in the frame or b) a 737 has been photoshopped in.
Pic #1 is a close up of the area right behind the post or stanchion thing. It clearly shows a long, thin white object with some billowing puffs of white smoke behind it. Look closely at the front of the white object. Vague jet airliner window shapes? The whole front section seems to have been thickened up a bit compared to the rest of the object, which looks pretty straight and thin.
Pic 2 has the object outlined. Of course we cant see what is behind the post, but the front and back could very well line up straight.
Pic 3 is the traced outline of a 737 200, made roughly the same length as the white object's straight edges. Not a real good fit.
Pic 4 is same outline of 737 shrunk down so the nose is the same size as the nose on the white object. Shame about the tail.
Conclusions: Sloppy photoshop job. It was too hard, time-consuming or whatever to accurately add a complete, recognisable 737, so they just fiddled around with what was already on the video frame, making it look ever so vaguely like a passenger jet by adding a barely recognizable nose and a bit of a bump on top.
Now I know this has been done to death, so flame away if you feel like it. Remember that as the outrage at the *Bush admin spreads and strenghthens, there is an ever increasing audience who are open to the possibility that 911 did not happen as we were told and it may just be necessary to patiently educate all the new converts.