Yes, in ”Archive” you can see the images you’ve uploaded to the system for later as well as those that appear in your templates.
If you want to discard images that aren’t in the system or your templates, you’ll have to edit the email in which they appear. Open the image dialogue and go into the menu. There you’ll find the option of deleting the images. You’ll only be able to see your own images and images pictures that have been uploaded to the same Publication.
The reason you can’t see all the images in the system has to do with permissions and security.