[#165] Add clearer border to blog images

Fixes #165 

![screen shot 2014-10-28 at 10 49 18](https://cloud.githubusercontent.com/assets/282788/4807050/1c8ef83c-5e90-11e4-99d6-20a3ef06f22e.png)


<!---
@huboard:{"order":937.0,"milestone_order":166,"custom_state":""}
-->