Please note that from the Q3 2011 release of the RadControls for ASP.NET AJAX, the RadButton has a property DisabledImageUrl. Via this property you can set a image of your choosing for the disabled state of the button control. In addition to this you can remove the transparency effect so that the RadButton image appears active when it is disabled, as you requested. This can be achieved by specifying the CssClass property of the RadButton with a CSS class that has the following structure:
For your convenience I have attached a sample page, implementing the suggested solution. Please use it as a reference for your further development.
All the best,
the Telerik team
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