This is not legal advice, and jurisdictions differ. But the shape of the answer is consistent enough to be useful, and it is simpler than people expect.

The mark is not the right

Copyright exists from the moment a work is created. A watermark does not create the right and removing it does not remove the right. So the question is never "was there a watermark" — it is "do I have permission to use this image". If yes, removing the mark is housekeeping. If no, removing it changes nothing except how obvious the infringement is.

Removing rights information can be its own offence

This is the part people miss. In the United States, section 1202 of the DMCA separately prohibits knowingly removing or altering copyright management information — which can include a watermark identifying the owner — where it is done to conceal infringement. Similar provisions exist in EU law. That is a claim in addition to the infringement itself, with its own statutory damages.

Usually fine

  • Your own photographs and artwork.
  • Images you generated, where the mark is the generator's branding — subject to that service's terms.
  • Licensed images where you were sent a marked proof by mistake. Ask for the clean file; it will be better than any repair.
  • Work made for you under a contract that assigns you the rights.

Not fine

  • Stock previews you have not licensed. The watermark is the paywall.
  • Another photographer's or artist's work, including "just for personal use" — reposting is publishing.
  • Anything you present as your own or resell.

Provenance marks are a separate question

Marks that say "this was generated by a machine" are not ownership claims, so copyright is the wrong lens. They are honesty signals, and regulation increasingly treats them that way — the EU AI Act requires disclosure of synthetic content, and platforms label it independently. Cleaning a generated image for a wallpaper is nothing. Presenting it as documentation of something that happened is a different act, and the law is moving toward saying so.

The practical test

If you would be comfortable telling the image's creator what you did, you are almost certainly fine. If the honest answer is that they would object, no amount of technical ease changes what it is. When unsure, ask — most creators say yes to reasonable requests, and a yes costs nothing.