Lets analyze the facts of the matter:
1. The Iranians claim to have downed a US Stealth UAV RQ-170 with minimal damage.
2. NATO has acknowledged that one of their drone is missing, last seen near the Iranian border.
3. US Military Sources say to the media that they believe Iran has the missing drone.
There are a lot of interesting questions here:
Do the Iranians have the drone in a condition that allows them to reverse engineer it? Or did it crash in Iran so nothing spectacular can be gained by examination of the wreck?
Do the Iranians have the capability to take control of US drones? Did they develop this capability themselves or acquire it from a third nation eager to test it? Or did they manage to down it using conventional methods? Or did it just crash due to some malfunction?
Lets suppose for a moment that the drone was shot down using conventional methods or malfunctioned and crashed inside Iran. It would make much sense for Iran to announce to the world that they had the ability to take over US drones! If US took this seriously (and it would be prudent for them to do that) then this would cause them much headache. They would have to spend a lot of effort to inspect all their drones and their control systems for suspected malware. They would probably temporary down all their fleet pending such an inspection (I would be surprised to learn that they have some drones operating for at least few days after the announcement). They would then need to factor in the compromise of technology and even adjust their tactics to some level. Perhaps they are aware of some vulnerabilities of stealth technology that will come apparent to persons that have the oppertunity to reverse engineer an almost intact drone.
Lets now suppose on the other hand that Iran did actually down the drone using some take-over method. They have the drone in prime condition and can look at it all they want. It would not really make sense for them to advertize this fact to the world, would it? It would be very easy for them to just say that they vaporized a spy plane that invaded their airspace and warn that other planes would receive the same fate. They could then, in secret start to reverse engineer what they have and gain further tech from it.
They could also keep their capability of taking over drones a closely guarded secret. It is entirely likely that this capability would come in handy some day and then the element of surprise will be most welcome.
Based on this, and the lack of any visual evidence, I think it is more likely that they are bluffing, that they do not have the capability to take over drones. And further more it is more likely than not that they just have a crater with some bits of drone in it. Lack of pictures supports this theory.
Then again, if they had this capability and wanted to test it, and wanted to hide this fact from the US, perhaps it would make sense for them to behave in this way. Whether the Iranians have the drone or not and whether they have the downing capability or not, I think the best action for Iran is to produce no pictures of the crash. This will drive the US intelligence people (gambit?) nuts until they get confirmation on the capability (or the lack thereof) by some other means.
This is starting to sound like a poker game and Iran is probably playing their cards the best way they can. I Wish I had the oppertunity to look at their cards over their shoulder
Bottom line is, we are not going to see any pictures of the downed plane any time soon. This would not in Iran's interest regardless of whether they have it or not. Why do I say that?
I. If they have the drone (almost) intact it would be in their interest to have US believe they are bluffing.
II. If they don't have the drone, or just wrecked pieces of it, it would be in their interest to have the US believe otherwise.
Of course the comments by the US military sources saying that yes, they believe that Iran has the drone must have some purpose. I guess they are trying to get Iran to produce some photos so they can now for certain. The uncertainity is probably much worse for them than actually knowing which it is.
Releasing pictures at this point by Iran would be stupid, and I don't think that the Iranian military is run by stupid people.