Downloading an image and displaying it won't work on Android

Hi,
I've been stuck on this for a week now but cannot seem to get this to work on my android device. (it works in the editor just fine).
I'm basically building a small app for my children that acts as a fake bank account, and rather than constantly updating the app I just want to grab a hosted png image and have it display.

I previously asked this question on Unity Answers by with no luck. I was wondering if anyone on the forum could have a look for me?
http://answers.unity3d.com/questions/1279075/downloading-an-image-displaying-it-wont-work-on-an.html
Many thanks