Aww poor baby, this looks sore. I'm not sure 100% what this would be, but it could be a hot spot, that may be infected or a staph infection? Not sure, but soaking the area in apple cider vinegar and warm water or Epsom salts and warm water may help. What has the vet said it is? Has the vet done a skin scraping to diagnose it? What type of medication/creams has he given you to treat Captain?