This is a really quick post and fix, I noticed my images were showing as broken links shortly after installing Jetpack. They were working fine at first, but then stop so I backtracked and found the cause of the problem.
It was ‘Photon’, if you have recently had the same issue, have installed Jetpack and activated Photon go back and deactivate it by clicking the ‘learn more’ button. Since the images that had broken were using TimThumb (my thumbnails), I assume the problem is with TimThumb compatibility rather than the module itself, so if you’re not using TimThumb it should work fine!
In the meantime if you wanted to use a CDN, check out ‘Cloud Flare’.