Is there a way to make sure that Google doesn’t find these pictures on my website anymore?
I would just ignore it.
As your website is sending the correct HTTP status code (404) for these URLs, Google will eventually drop them from its index.
There’s a link removal tool in GSC, but here’s what Google says about when NOT to use this tool:
To clean up cruft, like old pages that 404. If you recently changed your site and now have some outdated URLs in the index, Google’s crawlers will see this as we recrawl your URLs, and those pages will naturally drop out of our search results. There’s no need to request an urgent update.