I made this user style to help fix that problem by outlining images, and also make it so when you click an image it expands over the page at full size up to the width of the screen.
Though it’s not perfect. If the image is already black it’s hard to tell. You could change the outline color to something less common, but that looks ugly. Changing the boundary radius would probably be the best, but it’s already marked as !important so I don’t think I can change it. I’m open to suggestions on improving that part.