Things there are at least 5 billion of: people on earth. Stars in the sky. Microbes in a human body. And, now, photos on Flickr.
The photo-sharing site has taken the internet by storm since it launched in in Canada in 2004. It was bought by Yahoo! a year later and quickly became the web's number one place to share holiday snaps. And last week it received its five billionth upload, a picture of Woodward College in America, by a young man called Aaron Yeo.
Oddly, Flickr wasn't originally supposed to be a standalone website at all. It was launched as a feature for users of Game Neverending, an online role-playing game its founders ran. It quickly proved, well, better than the game, and the company switched its focus to it.
Probably just as well. Here's to photo number six billion.