These requests are probably made by search/indexing bots. My personal server gets a quite a lot of these, but they rarely use any bandwidth.
The easiest choice (probably disliked by more savvy users) is to just enable cloudflare on your server. It won’t block the requests, but will stop anything malicious.
With how advanced modern scraping techniques are there is so much you can do. I am not an expert, so take what I say with a grain of salt.

I believe the difference is how old the original artworks are. Someone copying the style of Mozart is appreciating his music, but someone copying a modern day musician is just breaking copyright law.
You can be inspired by Picasso or even Bob Ross, but you are copying/tracing an artist from Tumblr.
In a way AI is just pastiche, but frownd upon.