This morning an insider from the Tory war-room confirms that the photo had indeed been "shopped", and provided us with the original from which the Tory war-room worked. Compare and contrast.
The Fake Harper

The Real Harper

A couple of key points:
1) Most notably, the fake Harper is too thin, whereas the real Harper possesses an upper-body that seems fuelled by anabolic donuts.
2) The real Harper is clearly talking on a phone to nowhere. My source tells me that there is an aide to the PM crouched behind that chair, whispering in a low, mellifluous tone: "Yes you Can, Mr. Prime Minister, Yes you Can!!
3) The real Harper has been known, when travelling, to remove whatever art work decorates his hotel room and replace it with pictures of himself. My secret war-room source tells me that these pictures have themselves been "shopped", to make Mr. Harper appear thinner.
Thanks to secret source and h/t Imp.