We should be liberal about accepting file URLs which might not be in the usual, canonical format. Basically, we should let the users paste links from any workflow ehere you might "copy image link" or copy from the location bar. For example,
- https://de.wikipedia.org/wiki/Wikipedia:Hauptseite#/media/File:Begin_CEST.svg
- https://upload.wikimedia.org/wikipedia/commons/3/35/Begin_CEST.svg
- https://upload.wikimedia.org/wikipedia/commons/3/35/Begin_CEST.svg?download
- https://upload.wikimedia.org/wikipedia/commons/thumb/3/35/Begin_CEST.svg/1024px-Begin_CEST.svg.png