I'm trying to say that copyright restricts copying, not using. If you publish something on the internet, you implicitly give people limited permission to copy it so their browser can download it. Once it's on their computer, they're allowed to look at it with one eye closed if they choose, or even to modify it for their personal use or set it as their desktop background.

The only reason you are allowed to modify a copyrighted image for personal use is because that's considered fair use. The fact that you found it on a website is irrelevant.

Copyright literally restricts using the material. If you buy a book, you cannot sell tickets to an event where you read it out loud.