Random images from Flickr aren’t very random. I saw this before, and recently noticed it again, while using random images for my Facebook profile.
I have around 11,000 public images on Flickr. It seems that picking a few disconnected images out of this pile is an easy thing to do. Not always so. For my Facebook profile I decided to show 10 random pictures. More often then not, I have two images from the same set or from the same photo shooting. Sometimes, I have to pairs like this!
I mean, what are the chances of getting your hands into a huge pile of pictures and out of 10 draws, get two images which belong together, and then do it once again? Not much. But Flickr badge does it easily on this blog. And Flickr application does it as easy on Facebook. And the problem is common because both of these rely on Flickr randomness.
Here are a couple of Wikipedia pages for further reading: Random Number Generator, Random.