lkjh098 said:
It seems like this could be automated for uploads using the bookmarklet, since it has the URL of the containing page at the time of upload.
Tumblr links would be wrong if you open an image from your dashboard or a reblog.
It would also point to
*tumblr.com/image/(number)
instead of
*tumblr.com/post/(number)
Though this could be automated.