Mairo said:
So how would smart source field work exactly? It detects direct URL being from inkbunny and starts flashing with example of needed URL in source section?

Pretty much yeah. The Upload from URL example should be a direct URL like https://data.site.com/file/#####.png. The Source URL example should be https://www.site.com/post/###. If the user enters a direct URL (https://data.site.com/file/#####.png) or gallery URL (https://www.site.com/artist) instead of a proper source URL it should automatically add a source field and emphasize the example https://www.site.com/post/### by changing text color or something.

An even smarter system might be site specific, for example if the user is uploading from https://d.facdn.net/art/artist/#####.png it could change the Source URL example to https://www.furaffinity.net/view/###. This makes it very clear what kind of source we're looking for.