How does one find a list of instances that aren't federated with meta?

And if they go through it enough to get enough accounts to upvote themselves to get past the barrier then it'd be easier to forensically find all their accounts and shut them all down. It'd make them lose a lot of time enough for a deterrent.

Just a suggestion but how about making a barrier of entry to post images? Like >5 posts with >5 up votes and 48 hours will unlock images functionality? It won't be a silver bullet but might make it annoying to create multiple accounts and participate enough.