The BBC is now showing what it says is another picture from AFP of the aircraft being downed:
Turkey 'shoots down Russian Su-24 jet at Syria border' - BBC News
However, to me that looks like an Su-27 or derivative, not an Su-24 (which the other pictures clearly do show).
Either two planes are down or, more likely, somebody is getting confused, spoofed or carried away.
EDIT: And now withdrawn by AFP, accepting it's an old picture.