You can't say you NEVER know. Just go by the rule of thumb. If it's being distributed on the Internet, and it seems outlandish, bizarre, or even highly improbable, it probably is.
I am an architect so everyone and their dog has sent this to me. The detail bubble (the circle with the numbers in it) was photo shopped on to the step, the first version of this I saw didn't have that lovely feature.
Ok, thanks!
You never know with photos these days...