2.2.0 Remove ALT tags from invisible images

ALT text on an image is meant to improve accessibility. For example, a photo of Queen Elizabeth deserves ALT text that says "photo of Queen Elizabeth". But if an image on your page is invisible, or has no meaning, don't include ALT text. For example, an old-school non-CSS-based layout will often use a lot of "spacer GIFs" to nudge elements around or hold elements to a minimum size. You may be inclined to add ALT text to these... but if you put that page through a screen reader, the electronic voice will read "spacer, spacer, spacer..." which is not only annoying, it decreases accessibility.

If you don't mind failing validation, to save a little bandwidth, omit the ALT attribute entirely on images that are invisible or meaningless.