Setting String as Image Source in C#

You need to specify an ImageSource instead of a string when doing it from code:

Uri uri = new Uri("...", UriKind.Absolute); 
ImageSource imgSource = new BitmapImage(uri); 
myImage.Source = imgSource; 

Unless I've not found the right part of Scott's post that you're looking at, he is binding image source to a url.

Specificaly,

ImageSource = tweet.Element("user").Element("profile_image_url").Value

Which would be something like

http://a0.twimg.com/profile_images/1158022545/mickn_normal.jpeg