With the advent of custom report items in SQL Server 2005 Reporting Services, you can implement your own report “controls” to, for example, render the value or the trend of a key performance indicator (KPI) as an image or use a chart type that is not supported by the native Reporting Services chart region.
Then, your custom report item (CRI) can be used just like a native report item. You can, for example, bind it to a report dataset to display a field value graphically. As you can imagine, custom report items redefine the concept of a standard report and open a new world of possibilities. This server extensibility feature introduced in Reporting Services 2005 (RS 2005) provides the ability to develop custom report items for embedding in reports.
For more information see How to do it in SSRS 2008: http://blogs.msdn.com/robertbruckner/archive/2008/12/31/customreportitem.aspx
and a great sample with code: