Greetings from Elmer
Hi! I am Elmer, the Thinglink Image Fetcher. If you see me poking in your HTTP logs it is because your user has signed up for Thinglink and is tagging images. I look at all of them and try to figure out which ones of them look the same so that the poor user doesn't have to tag every single one manually.
I do also do some other things, like try to make sure the user actually tries to load an image, and not, say, a PDF file, or perhaps a piece of toast. (Mmm... toast... with jam).
I don't store the actual images; I just store some data about them - and occasionally I may cache a tiny thumbnail for some of them for some time - and I try to be nice to your web server. If you don't like what I'm doing, please drop a message to firstname.lastname@example.org and we'll be extra nice for you!