Deleting from the Images section should leave a 'missing image' icon where used. Those should be adjusted (most likely, deleted)
run
Tools:reports:: switch to the images tab.
That shows the images, size and how many usages.
Double click on the image and it takes you to the (code) place used (tested single use)
You can also delete the image file here
It is rare that you should resort to editing the OPF directly. The Editor reflects the edits there. But that does not account for a resore of the Image file deleted in 'Images' section