AddDirectShowSource is used when developers are building their own Filter Graph and do the rendering. Once a file has been successfully imported, the user has a DicomImage returned from that call, then he can call AddDirectShowSource to add this imported image, as the SourceFilter, to a given graph. An IPin interface is returned, representing the output pin of the newly added source filter. The user may later add other filters to compress/decompress and then render the image.
Example code about how to use AddDirectShowSource can be found in Mpeg2_Support