In my experience, the image link from Tumblr posts is not helpful in manually going back to an artist's Tumblr (unlike deviantART, where the title and artist are in the image URL). But, I'm not sure what would be the preferred link to use. Right now, I've been combing back through the Kuitsuku uploads, and say for post #1444520...
Direct URL = http://25.media.tumblr.com/tumblr_lrca2wQn1G1qcuvc5o1_1280.png
Photo URL = http://kuitsuku.tumblr.com/image/10066660337
Post URL = http://kuitsuku.tumblr.com/post/10066660337
I've been slapping the Post one on (with the direct link sitting the the tag history), but maybe the specific photo URL would be preferred, when available, especially from posts with more than one image.
However, doing a search, saw Log post in topic #8324 to leave Tumblr links raw (or more specifically, that only Pixiv and dA links are redirected), since changing the link would mess with how bookmarklets(?) detect if an image has been uploaded. That was 11 months ago, so what's the current stance (before I do more damage)?
<thanks for the redirect, Toks>
Updated