It doesn't work if you disable image loading.
For 90%+ of the web browsing I do, I don't need to see images at all, and browsing using emacs-w3m which I have set up to show only text and not load any images suffices. Occasionally there might be some image I want to see on a website and then I'll usually load it and view that one (or handful of images) manually. Very very rarely, I'll visit a site with an image gallery, where loading and viewing images one at a time is too painful, and then I'll just open it in Firefox, which I have set up to load images.
I know not loading images by default is not a solution for most people, but it's worked great for me for many years.
Update: A lot of replies are mentioning CSS. Just for the record: emacs-w3m does not process CSS
Wouldn't affect you with since I believe w3m also doesn't ship with CSS. But if anyone is reading this and thinking, "ah, disabling images in UMatrix will do the trick" -- probably not?
That's the real thing to take away -- that images are not the issue, the cache is the issue, and there are lots of things that can go into a cache beyond just images. If you're not caching anything, you could probably load images by default and you'd still be fine.