Well, the pilot appears to be missing in multiple photos from different angles. See below. And this fact supports, rather than refutes, that the picture in question is a non-altered image.
Just think for a moment--just a split second--about the tail wheel.
(1) If the tail wheel was photoshopped on (added) to the photo in question it would not appear in multiple videos and multiple photos that are not in question. Remember, the image [in question] was the very first publicized. Thus, it is not reasonable (or rational) to believe that someone would photoshop on a very strangely extended tail wheel AND THEN have every other photographer who took a picture of the same airplane do the very same thing.
(2) The skeptics theory holds that the vertical image was photoshopped from a horizontal picture of the airplane sitting parked. Look at the tire. The tire in the photo shows no evidence of compression--the weight of the tail of the airplane is not resting on the tire. Look at the picture at bottom. See how the tire is compressed?? It is not rational to believe that someone would take the time to seemlessly photoshop in a non-compressed tire. (How would someone get a picture of a non-compressed, extended tail wheel from a parked P-51 by the way??)
(3) Five (5) separate photo-manipulation analysis programs fail to detect ANY alterations to the image.
(4) On the other hand, look at the sky in the Difference of Gaussians, Sobel Analysis and Prewitt, not to mention, the Digital mapping and Inversion images. Note how both backgrounds (the sky) matches seemlessly between the two? It is readily apparent that both images were taken within a second of each other and from the same camera.