The best way to go is to create some sort of collection of the images you want to display, like a List, or any collection type that implements the IEnumerable interface, then bind the to the ItemSource property of the RadCoverFlow.
This sample gets its images from Flikr, but you can in the see in the code-behind (Example.xaml.cs) that populates a collection (an ObservableCollection in this case), and the last thing it does is bind it to this.coverFlow.ItemSource: