Hey
I had the same treatment on my horse a good few years ago. It was on the inside of his thigh and when it started to peel away it looked very similar to that. I had the vet out every couple of days to put the strong cream on then I had to apply some myself everyday, then every 2nd etc...
Imaverol is good but you need to make it up much stronger than it recommends. Bath the horse in it every two/three days. Wash everything tack/rugs your chaps/boots etc in virkon and disinfect your stable and bedding at the same time. Ringworm doesn't disappear over night and is a pain to deal...