If you look at the gal on the left...
Her pregnant belly seems to be airbrushed. The dress isn't partially spandex/elastic. That means, the dress would flow outwards then straight down... so you won't see anything showing the bottom. Secondly, you'll see that her feels are in an awkward position. By judging her height, she seems to be shorter... but the feet makes her look taller and makes the overall image of her look horrible. The cigarette in her hand looks too fake. If you look at her fingers carefully, you'll see that they're closely together... so there's not enough room for an actual cigarette to fit.
If you look at the guy on the right...
The top of his head looks real, but the rest of his hair looks fake like it was cloned. As for the teeth, it looks like his tooth was "blacked-out" to make him look like a homeless beggar. If you look at his arm, it obviously doesn't match the lighting of the overall image. Both of their faces show that the light is natural and outside. The arm looks like a picture made with artificial light. It's also too tan to be real. It looks almost as if it's a work-out arm and it was originally holding a dumbell weight instead of a beer can. Also, he's standing right next to her, but his feel shows that he's in front of her. That shows that the legs and feet are fake.
Finally, check out the dog...
Whoa... the lighting on the dog is way obvious. On the couple, the light seems to come from the top left. On the dog, the light seems to come from the right.