"While definitions have been tossed back and forth about the POW status of detainees, I understand that Saddam is specifically designated as a POW, and releasing photos of them for propaganda is against the Geneva convention. Somebody is going to get nailed for this. "

Maybe not.
If a soldier gave the paper the photos, then someone will get nailed, but I don't think that only soldiers had access to them. Saddam afterall has lawyers and lawyers have those working for them.
Soldiers could tossed in jail for committing such an act.
But let's be clear who the responsible party actually is and that is the paper the Sun. The only way that the Sun would be not guilty of a war crime is if Saddam's legal agent handed the photos to the paper.

Now, the Sun would need to paid for these photos, no? And if it paid a soldier, wouldn't there be problems with this in addition?
Tabloids are trash news, but I believe in general they are very careful about doing anything illegal. And I think that politicans if they could would be extremely eager to go after such publication as the Sun, much more so then say the Guardian.
So it seems that the Sun has made very dumb mistake, or they are playing on getting everyone undies in a knot, AND not face legal action.