I don't see any doubling. It's definitely not a proof. None of the proof wheat cents have a mint mark.
Hard to tell from that image . check and see if it has the extra eyelid . http://varietyvista.com/01a LC Doubled Dies Vol 1/DDO 1956-D.htm
The proper term is doubled die, not double die. But yeah it is hard to tell from this image can you get a better shot? And cannot be a proof with a with a mint mark considering it is a wheat back. However, it is not impossible. Hard to tell from this. It does look like it's doubled, but most likely md, because from what I can see, the reverse appears to have much of the same. Are the letters absolutely flawless, or do you see some type of gouges along the way? If it is flawless, and it is most likely MD. Need a better picture.
