Yes, two similar plastic chairs is a perfectly good reason to doubt it was real. I mean it's not like they mass produce millions of white plastic chairs. Going by those pictures you can't really see a damn thing. That site proves jack shit.

Don't be stupid. If they were going to boost war support they wouldn't fake beheadings. That makes the public want to get our troops/civilians the hell out of there for fear of losing a member of the family, or anyone else for that matter.