Well I don’t think all images would have to be signed, just photos for which you want to prove authenticity. Probably social media and dating apps seem like a good target. Maybe some advertising, sure. I bet McDonalds wouldn’t mind green checkmark since they go through all that effort to fake food in real life.
You could of course fake green checkmark in CSS but this is already an issue with faking other browser UI elements, including address bar–it’s a known problem.
One way to solve this is having a browser picker, that is a button you click in trusted area of browser UI that lets you inspect any image on the page. Similar thing is possible with smartphone UI, you go to app overview/carousel and long press on an image in app, this launches photo inspection portal.
You could of course fake green checkmark in CSS but this is already an issue with faking other browser UI elements, including address bar–it’s a known problem.
One way to solve this is having a browser picker, that is a button you click in trusted area of browser UI that lets you inspect any image on the page. Similar thing is possible with smartphone UI, you go to app overview/carousel and long press on an image in app, this launches photo inspection portal.