Here are the things I would try.
Copy the CHM to a portable medium such as a USB stick or portable hard drive. Try opening it up on a different PC. If you see images on a different PC, likely something is amiss with your own PC that needs to be addressed.
On your own PC, try opening a different CHM and see if images appear there. If not, it's further confirmation that something is configured incorrectly on your own PC. But if so, then it indicates an issue with this one project.
Give those things a try and report back with what you find.
Thanks for the help, Rick.
Someone opened the CHM on a different machine. The graphics are all still missing.
I opened another CHM, compiled with RH 11, on my machine. It displays the graphics just fine. Unfortunately, I do not have another CHM generated by RH 2015 to test.
Okay, so it is an issue with this project. One way to confirm is to click the File tab and open one of the supplied sample projects. Compile as CHM and see what results.
Interesting. I tried deleting one of the images and then inserting it again. It was named inset_3.png. When I click OK to complete the insertion, I get the message "Unable to rename file. File contains illegal characters". Nothing I do will make it accept the file. I've tried completely renaming it something different, same message.
I opened the sample project Travel the Whirls. The graphics appear in the project. When I generate the CHM, they do not appear.
Sounds like you might need to download a diagnostic app called "MJ's Diagnostics". Likely something has "come undone" such as a DLL becoming unregistered.
This is a free download and it's offered by a fellow former Microsoft Help MVP.
Give that a go and see if that helps.
I have just acquired the same problem using Robohelp 10. A project that was, until today, generating images perfectly fine in Webhelp output, now only gives me little red crosses in empty boxes. Other projects, run on the same PC, generate with no problem.
This doesn't help you, but I want you to now you're not alone in your misery.