It's really hard to tell. The old heaps parked in the photo tend to shout "20's and 30's", but the car in question surely does look post-WWII, so it seems to be some sort of mirage.
The Buick Roadmaster is a good guess, but the complete absence of any other post war cars in the photo tends to peg the photo as being taken before the Roadmaster was produced. Perhaps if the buildings (and location) in the photo could be identified and dated, that would help pin down what's going on with the mystery car.
Other possibilities might include a 30's concept car sitting in front of a dealership, or a four wheel teardrop travel trailer.
Or maybe someone just got creative with Photoshop to annoy car buffs.