It doesn't look like the pox pictures. To me it looks more like a fungus.
Pox pictures.
This would be my guess.
RINGWORM (FAVUS)
You’ve probably heard of (or had) ringworm, a fungal infection of the skin that people and pets can catch from each other. Chickens can also get ringworm and share the fungus with their flock keepers. (Here’s a tip for word game players:
Favus is the name for ringworm when it affects poultry.)
Ringworm usually appears as white scaly or crusty patches on the comb and the skin of the head and neck. The chicken may lose its feathers, typically starting at the base of the comb and progressing down the back of the neck. Other than the skin problem, affected chickens are usually healthy. The infection is contagious and spreads from bird to bird, and rarely, bird to human.
Any practicing veterinarian can do a skin scraping and fungal culture on a chicken to diagnose ringworm, the same way the fungal infection is diagnosed in other animals. If you have a chicken with favus, isolate it from the rest of the flock to prevent spreading the infection. People should wear gloves and wash their hands after handling the affected birds.
Rubbing the affected areas daily with athlete’s foot ointment, or swabbing the spots with 2 percent iodine solution every other day should do the trick after about two weeks of treatment. Both medicines are available at any pharmacy. Ringworm fungus hates sunshine, so getting birds out of a dark shed and into the sunlight often cures favus without medicine.