The documentation (http://msdn.microsoft.com/en-us/library/53ezey2s%28VS.80%29.aspx) indicates that it returns null if it reuses an existing process and no new process is started. If you can't find a way to get a reference to the process that is displaying the picture, perhaps you can use a TempFileCollection (http://msdn.microsoft.com/en-us/library/system.codedom.compiler.tempfilecollection.addfile.aspx) to clean up the images when the application exits.