Untamed said:
It's been proven that it can be done, direct linking an image from furaffinity adds the artist's page and submission link to the list of sources.

Why can't it be the same for Pixiv, etc.? It really doesn't help that, on top of the sourcing not yet being automated, the direct link is purposely munted to give you a 403 error.

It does not. Furaffinity is one of those pages where you have to remember to add source manually.

Automation right now is based on information available from URL. With furaffinity URL, the direct image URL does contain artist account name, but not submission ID, so that's why it only autofills artists gallery link, where something like pixiv doesn't have any information like this.

Pixiv also has hotlink protection that will give 403 error, but e621 upload form has referral set correctly and accepts those links.

Also if you are already using direct URL upload, changes are that you are at the very submission page which will only take a second to copy as well, where manually doing that afterwards can more than several minutes and coding something that would crawl the URL would take not only insane amount of effort but also insane amount of computing power for something that everyone uploading should be doing.

And this was kind reminder that I and others need to manually fix all and every source of your uploads.