All images on getpersonas.com are cached forever, so timestamps are added to the end of the image urls to allow for updates. The modified timestamp column is stored in the personas table. Example: http://getpersonas-cdn.mozilla.net/static/7/0/81070/preview_large.jpg?1264100589 This is used for thumbnails, header and footer urls.

Turns out this isn't that simple since we're syncing db's. We currently grab all valid personas, then subtract the personas we don't want to sync. To do this we'd need to grab a 3rd set (valid personas that are modified) and .union() that in. This is a P5, so it's outta this milestone.