Queston is, how did he do it?
I got my two avatars and changed the contrast on them to 0 so they were a solid color. Next I colored one the blue from the forums then I colored the other the white from the forums. Each of them on their own layer. Next I make a checker fill pattern and deleted all the white squares then selected all the black, I switched layers to the first avatar and deleted the area the blacks used. Then I shifted the grid over 1 space the deleted it on the other avatar. Delete the grids and flatten the images and viola. Combined avatar thigny.