This is the thing that's wrong. No it's not defacing it but it's my property, changing it without my permission is not only unacceptable but also illegal. I don't mind people extending it if they ask permission, doing it without permission is what is wrong. It's people with outlooks like yours that's the problem.

"I think I can improve this picture, it's not mine and I haven't asked permission but I haven't defaced it. I've done nothing wrong."

Correction, you are a thief and have committed a crime. This is why thieves get banned on here, it is illegal. A criminal offense is not just about defacing things.