They are split down the middle and then mirrored images - Rummy seems to work the least well of all of them. Interesting that people normally find people that are symmetrical that way more attractive - and people tend to vote for people they are more attracted to.
the pic they used for him, he was turned slightly, so when mirrored gives him the look of a huge forehead that is collapsing - I've never noticed his canine teeth before, so those are probably photoshopped as well. His nose gets a defined ridge and his eyes are too close together - as a result, he looks the most off of all of them.
I'm curious if how he looks with a better starting pic.
Models tend to look exactly the same if you take either half of their face and then mirror it. Joe Slob on the street tends to look entirely different when they do it, and sometimes slightly off.