When using AI generated images no one should be an infringer since copyright shouldn't apply to AI's output. People should be able to use AI generated images already created without fear of infringement, but you're right in that it requires you to be able to identify a work as being AI generated. Edit's to an AI generated image shouldn't make it copyrightable so photoshops and recolors wouldn't matter, but repainting an AI generated image entirely by hand could arguably give an artist the ability to copyright the specific reproduction, to the extent that if I repainted the Mona Lisa by hand I should have copyright protection for my re-painting.

The difference between using Midjourny to create an image and using a brush in photoshop is that the line generated by the brush tool in photoshop wasn't dependent on countless other copyrighted works while the image generated by Midjourny was.

Since copyrighted works were exploited in the creation of images created by Midjourny in a way that makes it impossible to credit or compensate the authors of those works we can resolve the issue entirely by preventing any of the art it creates from being protected by copyright. Artists whose work was used to train AI can rest assured that no one is exclusively profiting off of their work without compensation. The sum of all art created by human hands throughout history goes in, art free for all of humanity to use without restriction comes out.

Anyone can use both Midjourny and photoshop to make an image but the resulting image wouldn't be able to have copyright protection, still, the image wouldn't be at risk of being accused of copyright infringement either. That frees everyone to use the powerful new AI technology to create artistic works without fear, but also without the protection of copyright.

Once again though, that'd require us know when an image was generated by AI even if edits were later made after the fact which may or may not be possible causing some people to get protection for works when they shouldn't, but even that would mean people who could prove their works were AI generated would be safe from being accused of infringement which solves one the big legal problems AI images have caused currently.