This article explains how to change the shape of the RadImageButton.
The RadImageButton can have a different shape depending on the image or images that are used.
This button shape should be used when you want to provide different images for the different states. This way
the button will take the shape of the image that are provided as a RestStateImageSource and
when the button is pressed, the button will take the shape of the image provided as PressedStateImageSource.
When you want to have a single image with transparent background you should use one of the other Button Shapes.
When the ButtonShape is Rectangle, the button will look like the native button and will have sharp edges. In order to see the shape, you can set the BorderThickness property to a positive value.
The default value of the ButtonShape property is Rectangle.
When the ButtonShape is Ellipse, the button will look like the buttons in the application bar.
Again, only one image is used and this image must have a transparent background and again you can use the BorderThickness property to make the button more similar to the buttons in the application bar.
Here is an example:
<telerikPrimitives:RadImageButton ButtonShape="Ellipse" />