This is a question for one of the members of the Cover Image Group. It's not a big deal but I thought I should ask for own my amusement. :)

I have two books in my Account (one I sent and another I requested) whose cover images keep changing back and forth. Why does this happen?

It seems as if every time I check in (which happens several times a day), one or the other book has a different cover. If I were doing a drinking game everytime this happens, I'd be drunk by now. :)

The books in question are  The Girl with the Dragon Tattoo and Just Like Heaven. Here are the covers that keep switching back and forth:

I have also seen the same thing with Slammerkin.

I've seen that happen when I have submitted a new cover image for a book that already has one. It keeps switching back and forth between the old image and my image for a while until it finally settles down to my new image. I figured it was because there are multiple databases that store the images (distributed, for maximum availability), and it takes a while for the new image to propegate throughout the system. (I also see a funny mix of the new and old image in the small, medium, and large sizes -- as in the small might be updated, but the medium isn't, etc.)

The site uses the Akamai Edge network to cache graphics. Akamai has a bunch of web servers all over the world, and some code that can route your request for a file to the server that will be able to respond the fastest. The first time a PBS member requests an image file from each Akamai server, it's downloaded from PBS. The Akamai server saves the downloaded file, and after that everyone else that requests it gets the saved file.

If you see graphics switching back and forth, it's because the two servers closest to you retrieved their images at different times. Eventually, whichever one is older will get a fresh copy and then the switching will stop.

Interesting!

This had never happened to me before and it's been going on for over a week with the book that was requested from me.