Not leg mites. You'd see the scales lifted up with what appears to be dirt under them. What this looks like is pecking injuries becoming infected.
Have you seen this chicken peck at their own legs or another chicken doing this?
I can't tell you for certain what this is, but I would treat them as wounds with regular soaks in very warm Epsom salts. And keep the legs greased up in between soaks with coconut oil, castor oil, or an antibacterial ointment.
And watch to see if this chicken pecks at its legs or if another chicken may be doing it. Also, go out to the coop at night and check to see if there are bugs swarming the roosts. These could be bug bites.