Back in March flickr introduced a similarity feature into its image search. Its a little hidden, which is my excuse for not finding it sooner, but any image that is part of search (normally using the search feature with the magnifying glass icon) will have three dots (…) in any image you hover over in the displayed search results. Clicking on the dots will bring up the search for similar photos feature.
So what does it do, simple it attempts to find similar photos. What makes it a little different to other offering is it uses Artificial Intelligence to help determine the subject, style, colouring and other attributes using neural networks. This is like google images showing visually similar images but flickr use their own similarity pivot technique (there is a lot of detail to be found in the article linked above). Flickr have also been putting these neural networks to good use adding/suggesting tags for your photos when they are uploaded. Flickr also has a wonderful resource of photos to look through. It isn’t perfect but it is very impressive.