If the PNGs are in your topics, they must be in the project folders somewhere. When you insert the way you did, RH will save the PNGs in the root of the project. Take a look there.
Also RH does not delete images just because you are not using them. It doesn't show them in Project Manager but they will still be there in Windows Explorer.
Also your CPD will have grown but DO NOT rename or delete it at the moment. Wait until a patch is released, probably later this week. You can track when by following the announcement above the list of threads in this forum.
I suggest you make a backup now and again after you have tidied up.
See www.grainge.org for RoboHelp and Authoring tips
Follow me @petergrainge
I did find the PNGs in the root, as you suggested. I must be tired today!
As for the rogue BMPs, I'm not sure why the Unused Files report didn't locate them. I cleaned up manually.
As if BMPs wasn't bad enough, I had a corrupt TOC that was doubling the size of my output. I found a past post that was very helpful.
Again, thanks for your help.
Replacing BMPs with PNGs will not have a great deal of effect on the CHM file size, since during CHM generation all the content is compressed. Thus the BMPs will be scrunched, while the PNGs, being already compressed, are hardly affected. That's not to say that replacing is a bad idea; BMP is an ancient format and PNG is better in many ways. But CHM size is not one of them.