I found a great utility plugin to help with adding a Image picker field to a widget. Basically you install and activate this plugin and you make your own widget and utilize the image field easily.
The only problem I had was that it didn’t work in Firefox. I found a simple error on line 72 in the scripts.js file. Instead of calling events.target.href it should be e.target.href because e is the parameter passed in.
how to use: http://mondaybynoon.com/20120206/wordpress-widget-image-field/