Genjar said:
No need to check the ones that aren't either source:tumblr*1280 width:1280 or source:tumblr*1280 height:1280, so that'll narrow it down a bit. Still 14000 posts, though...

And since most posts aren't sourced directly to the original anyway, it might be worth checking all of source:tumblr* width:1280 and source:tumblr* height:1280. Which is a whole lot of posts. :/

Kinda glad that I haven't uploaded much from Tumblr. Even so, this'll ruin my upload/deletion ratio.

I knew it!
Adding the direct link to the sources is good for something.