Add a check box in the SDK like "I'll be the only one using this avatar", then use that flag as an index to check how many occurrences of that said ID happen to be in use. If more than one instance, then flag the offended user for review and send an e-mail to the owner asking them to re-upload the Avatar to change the ID. It won't stop cache rip techniques though, but people who have the knowledge to do so is considerably lower.
-Credit goes to Kane on discord for the idea