Digging further, I discovered the following four subtabs under "Popular": "Interesting", "Views", "Favorites" and "Comments". The latter three were clear; indeed, they ranked my photos according to the number of views, times favorited by other viewers and the number of comments, respectively.
How could one define "interestingness", however? Surely it would be too cumbersome for whoever is running that Flickr establishment to go through half a million of photos uploaded on a daily basis, selecting the ones they considered the "most interesting"? It would not be particularly objective, either.
After some thinking, I assumed that "interestingness" was a sort of a blend of the other three parameters. A closer look at my own pictures signalled me otherwise though. The correlation there was far from perfect.
I then searched for the answer in Flickr's Help Forum. I wish I hadn't. The matter turned out to be a real can of worms, with fellow Flickrers complaining left and right about how their best photos were not deemed "interesting" and how the photos without any views were suddenly on top of the list. As if on purpose, Flickr staff did little to allay the users' suspicions. Indeed, the website seemed to draw certain pleasure in maintaining a veil of secrecy over the algorithm defining the notorious "interestingness".
The bottom-line is, I failed to find my answer. I may never find out how my photos were selected as "interesting" and who made the selection. I am also clueless about what I personally could do to affect the popularity of my pictures. Other than taking good pictures in the first place, of course.
Disregarding all that, I thought Flickr's selection was in fact not too far from the truth. And today, ladies and gentlemen, I present you the Top 50 Most "Interesting" photos by anjči! Enjoy.
The morale is that I do not seem to travel enough outside Europe. My planned trips to Mexico, Vietnam and Syria over the next nine months will hopefully balance the case. Stay tuned!