Although there are several possible benign explanations for the image -- such as a barely perceptable jiggle of the camera as it took the time exposure -- NASA's zeal to examine the photo demonstrates the lengths at which the agency is going to tap the resources of ordinary Americans in solving the puzzle.
Must have been a Klingon Bird-of-Prey that was cloaked that fired on it! ;)
S.F. man's astounding photo / Mysterious purple streak is shown hitting Columbia 7 minutes before it disintegrated