Image checking

Check to see if image is broken, then replace image with invalid image.  Still not sure if we should go with something a bit more jazzy for the invalid image, any thoughts @JakeChampion ?

![yes-github-yissssss](https://f.cloud.github.com/assets/1492067/2005143/c8bd4b18-86d2-11e3-886a-9e223a262b41.gif)