I have seen this on a lot of bunnies, including my own. It seems to be a healed sore hock. Once a sore hock develops, it seems that the fur never really grows back there and a pink, normal colored callous forms, like a dog or cat's paw pad. A lot of the bunnies at the shelter come with these. As long as it's not scabby, red, or feels like it's full of liquid, I wouldn't worry about it. I think the scar tissue that forms from a healing sore hock keeps fur from growing back in that place.
Both of the pics look normal and not like an active sore or infection to me.