IP: 35.187.51 (AWS, and all visits to date have used the identical aa.bb.cc.dd)
UA: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.81 Safari/537.36 PrintFriendly.com
Requests: all images (only) associated with a given page
Referer: the page the images “belong” to
Paradoxically the only reason I noticed this UA is that it lives in a blocked range; usually I don't pay much attention to image requests. Retroactive search through logs finds its first appearance in July.
I suppose it's a human tool, but the IP and UA belong to the thing itself, not to the human user.