This problem drove me crazy for a while:

I did a website for recently an established webcomic and some of the old archive images were showing up in negative on some browsers, and not showing up at all in others. But it didn’t happen to all the images, and not on all browsers. I beat my head against this for a while.

When you can’t figure out what’s wrong with an image, you look at the image properties, rather than beat your head against a wall. This is what I suggest, anyway, because I didn’t do that.

They were CMYK.

CMYK images show as negative in Safari, and don’t show up at all in some versions of IE.

Yay. Great. Converted them to RGB, re-uploaded, all fixed.