How do I make RoboHelp report missing graphics?

[RoboHelp 9]  Before building my CHM, I need to find out if any linked graphics are missing from the project's \graphics sub-folder. Is there any way I can make RoboHelp report missing graphics? The Broken Links report doesn't care if graphics are missing, only if hyperlinks are missing their targets. The Image Report just lists all the images referenced by the topics, but doesn't test if they are actually present in the required location.  And if I build the help, the OutputLog.txt does not report that an image was missing.  Any ideas how to detect missing images, before my CHM goes public?