I think it's problematic that both CSS and HTML attempt to define images for the web.

We need a central place that is responsible for fetching and decoding a byte sequence/stream (and dealing with EXIF) into an abstract representation of an image, that can then be used for various purposes. If we define this in different places in conflicting ways, the differences can lead to security issues. (Perhaps some of these concerns can be split, but an image being generated from an opaque response is an important property that needs to be part of the model and thought through whenever new features are added.)

See also #4929 and #5165.

cc @domenic