> even 1 MB is considered pretty large for a web image.

Compressed. Remember that in order to display it, the browser has to unpack it to what amounts to a bitmap. And newer, better compression formats (e.g. PNG) make that even worse in compressing the same bitmap file to a much smaller transmission size.

Did you consider compressed JPG/PNG on disk versus uncompressed raw image data bitmap in RAM?

A 1024x768 32-bit image is 1024x768x4 = 3.145.728 bytes when uncompressed.

Right: the example is contrived. My point is mainly that it is actually within reach, and that workload needs to be taken into consideration when making any statement about how much memory a browser should be using.

It happens to me all the time - the "linked images" bookmarklet combined with EarthPorn reddit + autopager.