A close-up in one area would be good; it is really hard to see from that distance. Is it only on the feet & ankles?
Also, I don't think you need to do a slice, perhaps, to start off try scraping off some skin either on or surrounding area to take a look. If you feel you need to go deeper than go for it.
Have you looked into the possibility of hookworms? They penetrate through the skin. You haven't said if you have animals around. This could be a clue too.