Crusty spots on neck, chin, and top of head

Hey guys,
To start, I have 5 cats. 3 are related as are the other 2 in question. They have these crusty scabs like things on their neck and head. 2 have them and 3 don't. Has anyone had this before?

Sorry, hard to get a proper photo of it

Fleas? Ring worm? Honestly I can't tell from that pic but those are possibilities. 

Do you see them scratching those area's quite a bit?  If so, it could be caused from food allergies. They tend to cause itchinss around the head and neck. Otherwise, it could certainly be flea dirt, but don't understand why it would only be in certain areas and only on two of your cats rather than all of them, if, indeed, there are fleas in your area.