Have you ever wondered how Flickr ranks your pictures according to Interestingness? I did a statistical study of my own 50 most Interesting images, similar to a study I did 18 months ago. The resulting model was quite good- (85% of the variance explained) so I am fairly confident in results.
So what matters in Interestingness?
1. Views, comments, and faves (no surprise!). A view is worth the least; a view and a comment and a view and a fave are about equal is worth; and a view and a comment and fave is worth the most. Of course to get good exposure outside your contact network, you need good title, tags, and text.
2. Notes added by others matter, a lot… although once you're over 5 or so I am not sure more matter. Galleries did not seem to matter, but that's a pretty new Flickr feature my sample is too small to observe its effect.
3. Posting to more groups is good, not bad, for Interestingness. My sample only includes images posted to between 1 and 30 groups. I'm not sure what happens when you post to 50 or 75 groups.
4. Posting to award groups is NOT good for Interestingness, all other things being equal.
5. Older pictures are less Interesting. Even if the image continues to pile up views and comments and faves, older images will be ranked lower in Interestingness, all else equal.
My results only pertain to differences in Interestingness between one's own photos. The question of why your image today is more Interesting than mine, or why your photo did or didn't end up in Explore, are more complex topics for another day…
Have a great New Year's Day everybody!