
Flickr has a very interesting stream called "Explore," in which they give a shout out to what they think are really cool photos.

The rankings in Explore for all dates change all the time even for dates in the past. Photos are uploaded to Flickr at a rate of around 400/minute and are constantly being viewed, faved, and commented by millions of members. Interestingness rankings are recalculated for all photos many times per day. Photos uploaded a day, a week, even a year ago, are still receiving activity in the form of views, comments, favorites, etc. And all of that activity affects each photo's Interestingness ranking, even for photos that were uploaded years ago. Explore is very dynamic. When you browse through Explore on any date, you are viewing what the Interestingness algorithm has selected as the highest ranked photos at that moment.
So to get your images on this selection you are competing with 500,000 additional images every 24hrs.
Lucky for me I have a ranking of 67 and 120 for these two images. Rankings change very quickly so you can be dropped at anytime.