Well, given that it just magically showed up in DeMohrenschildt's storage warehouse while they were in Haiti, a better question might be why do you think Oswald had anything to do with it?
Actually, George DeMohrenschildt thought that it might have been Michael Paine (who apparantly died March 1st) who placed the box containing the BY photo in his storage unit. If true it raises all sorts of questions about that photograph.
First of all, if I remember correctly, Michael Paine has always played down his relationship with DeMohrenschildt, so how did he even end up with access (key?) to his storage unit?
Secondly, Michael Paine has always denied that he knew Oswald had a rifle, but how could he not have known that if he saw/handled the photograph?
Thirdly, why would Oswald "give" DeMohrenschildt a photograph of himself showing him holding a rifle, which he allegedly had told George he had used to shoot at Walker? Was he so stupid that he was handing out photo's that could support an attempted murder charge against him?
And then of course, there was the handwritten text in Russian, which wasn't in Marina's handwriting?..
So, for a photo that was supposedly taken by husband and wife, there seem to be at least three other people possibly involved with at least that one photo. So, what was really going on?