Hi,
First of all GDI+ functions and classes are not supported for use within a Windows service. Attempting to use these functions and classes from a Windows service may produce unexpected problems, such as diminished service performance and run-time exceptions or errors.
So in your situation you can either write your own code to do the image conversion or otherwise, you can use the GDI+ from an interactive application and have the service talk to that application.
Hope the above helps.
Thanks
Saswati