Well, I was born and raised most of my childhood about a half hour from where Deliverance was filmed in Georgia (let the jokes commense). Hell, the lake in my town was there as a result of the river the characters were going down being dammed up...remember, beyond Ned Beatty losing his anal virginity, that movie is actually ABOUT something relevant...man's encroachment on nature, messing with things he shouldn't, etc.
My dad saw this guy in Ellijay (town nearest where the filming took place) in around the mid-80's ...said he was working at a place giving guided tours of what was left of the river. He's not actually retarded, just born with a really f-ed up skull/face.
So if you think about how this movie and the book were about the overdevelopment of a mostly-untouched natural and cultural area, this poster's pretty damned smart...maybe even conceptual...!!!