These are often said to be men from the American South or from Appalachia, and the photo is often used to make fun of US White Southerners or hillbillies’ tendency to have sex with, marry and make babies with family members.
Actually the photo is from The Cape Horn region of South Africa (the whiter and more Dutch part of South Africa even today), and was taken around 1993 by Roger Ballen. These are two Afrikaner brothers. The photo is often said to be a result of inbreeding, but that is not known for sure. All that is known is that they were both retarded, which seems obvious looking at the photo.
There are websites out there who will give you the names of the brothers, but I didn’t have time to look it up although I saw that information at one time recently.