Do you have evidence that it is not? If so, cite it. If not, why is your assumption that it is not authentic any more trustworthy than my assumption that it is? If you have evidence that it is not authentic, offer it. Otherwise, can the innuendo. It only reveals your prejudice. When someone offers evidence the photo is a fake, I’ll change my assumption. But I won’t change it based on your assumption to the contrary.
Dude, just look closely at the picture.
Well, for one thing, I'm a graphic designer and that is as horribly obvious a "Photoshop" (which I use daily) as the phony smoke over Lebanon.
Even the most casual of photographers can recognize the difference in light on the subjects. See how it's the same on the Romneys, but different on MLK? Also, look at MLK's jacket, between the mics. Doesn't it look a bit "unnatural"? Yes, it does. It's because the picture fraudulent.
So, my experience in my profession is my source. You can call it "prejudice" all you want. I call it "reality".