If you subscribe to the RadBinaryImage's OnDataBinding or OnPreRender server event, you will be able to retrieve the URL from the ImageUrl property of the control.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.