The photo looks legit, and there's no reason it shouldn't be. The vapor cloud around the jet is what is known as a Prandtl–Glauert singularity. A common misconception is that it appears only as an object passes the speed of sound. In point of fact, it can occur at subsonic speeds that are near the speed of sound. I've photographed it myself at military airshows where the jets did not break the sound barrier (no sonic boom). Here's more on the Prandtl–Glauert singularity:
For video of this phenomenon (which looks a lot like the same fly-by that produced this photo), check out this link. It's ranked the #1 low fly-by, so you have to watch to the end:
http://en.wikipedia.org/wiki/Prandtl–Glauert_singularity
For video of this phenomenon (which looks a lot like the same fly-by that produced this photo), check out this link. It's ranked the #1 low fly-by, so you have to watch to the end:
http://biertijd.com/mediaplayer/?itemid=19448*