I can't quite tell if this is still an issue on NGS due to MBS-1156, but this is a problem on current prod, so guessing it's still an issue in NGS.

Tried a test at http://test.musicbrainz.org/release/f2bf0f9d-d971-4df8-8e38-db7de1e9fa95/relationships adding a cover art link to https://www.cdbaby.com/cd/dsm

On current production the cover art fails to display on releases. Suggest that either the URI is cleaned pre-edit (with JavaScript) and/or the server is able to support HTTPS URIs. Since often certification validation for arbitrary sites can be an issue for client applications, suggest that perhaps cleaning the URIs is more sensible in the short term.