(split off from T116515, which solved this for videos from Commons)

Phabricator allows uploading images locally (to the separate domain phab.wmfusercontent.org, to be precise), and it appears that people find it useful to be able to illustrate tasks etc. in this way.

It would be nice to be able to embed images from Commons, too, e.g. for charts, screenshots, and mockups. As described in the Remarkup documentation, it's already technically possible to do that for YouTube (after setting a configuration variable), see also source code, and in T116515 it was implemented for videos from Commons. See T116515#3301860 ff. for some further notes about options to implement it for images.

Benefits:

• avoid extra uploading efforts for one's own files (upload them once to Commons, use both here on Phabricator and elsewhere), and the need to keep two version in sync (in examples such as this)
• enable the reuse of freely licensed Commons media by other users here on Phabricator

(Digression on licensing: The footer below optimistically claims "Content licensed under Creative Commons Attribution-ShareAlike 3.0 (CC-BY-SA) unless otherwise noted", but when I upload images here, I'm never asked to release that content under that license. So I'm kind of curious how that works legally. IANAL, but while the WMF Terms of Use specify licenses for text and - in the Phabricator ToU amendment - for code, they don't do so for other non-text media. In any case, a Phabricator media page - example - does not state a license and does not offer an option to specify an author separate from the uploader. Therefore it's not possible to satisfy the attribution requirements when reusing e.g. CC BY-SA media here.)

See also the more general task T186246: Allow hotlinking of external images in Phab tasks (basically the same for more arbitrary domains, except that or commons ), T76247: Implement ability to select Phabricator avatar from Wikimedia Commons, and upstream https://secure.phabricator.com/T4190 .