Something doesn't add up:

Facebook serves 570 billion page views per month

Facebook’s systems serve 1.2 million photos per second. This doesn’t include the images served by Facebook’s CDN.

That's an average of 5,45 photos pr. pageview, excluding CDN-served images.

http://www.google.dk/search?hl=en&safe=off&q=(1,2+mi...

Open your news feed, i get at least 15-20 photos. Go to a profile page, you see their wall and photo's they're tagged in for example. Most of the time thats above 5 as well.

I just did, and all of those are served from fbcdn.net.

If I remember correctly, Facebook uses the CDN as a cache for images, and loads from central servers when there's a cache miss. Even with a very large cache, there will be compulsory misses as new photos are loaded into cache. That might help explain their figures.

The CDN has to load them from somewhere.

Mmm, You're right, then I dont understand what photos they're referring to.