I never really paid attention to the GUID. We only have about 15 images, so maybe it's simpler for us. I also don't have unlimited disk space, so I'm forced to keep up with deletes so never deleting more than 2 or 3 images at a time.
When I'm ready to delete, I usually do it in the console first under All Resources, Software Component, Image Resource and make sure I have the name right I'm deleting (usually straight forward as I number images win7entx64v1, v2 etc so I'm deleting the old v number usually).
Then on the server, I have a shortcut to where images are stored in 7.5 on my desktop
\\cms\NSCap\bin\Deployment\Packages\Images
So I go there, then search that sharepoint for partial name to find what I want to delete, then go to that file location, go up a level to get to the GUID folder and delete.
Agree a report would be nice, but in case my way helps anyone, figured I'd share.