You have to state where the picture is coming from. If it is within the application, or on the internet, then all you have to do is bind the property to the source:
<image source="{Binding Path=Image}" />
Thus you have a property in your ViewModel that contains the path. For something in on of the assemblies you might want to have a path looking like:
"/Fox.UI.Shell;component/Images/WoodenBucket.png"
I believe you can also bind to a bitmap object.