Here "Source folder" is the path to the folder for which image file need to be created. this folder should exist on the system. In example you mentioned image file will be created for all contents under "c:\dell\drac_source" hence this path should exist with all required file for the image file under it.    "Image_file name" is the absolute path where the image file need to be saved. By default a path and foldername.img will be shown for this location. If you wish you can change it. This file should not exist while creating image as create image option will create an image file of Source Folder and save it as "Image_file name" When you tried did you give both "Source folder" and "Image_file name"?
idrac9 dell r740XD This issue goes back many years, and I am pulling my hair out (and I need it) It seems that to create an img file I need one to begin with (!?) create image ->  Source folder c:\dell\drac_source  Image_file name c:\dell\drac.img <"drac.img" does not exist> "create Image" -> failed "The image input is empty". Image Input??? Source folder or the image name??? The image filename that does not exist? What is it referring to? What am I missing?          
idrac creating/mounting an image