1. Edit ezpublish/config/config.yml, reset default image aliases and add a few test ones:
Note: in this case, the admin siteaccess name is "ezdemo_site_admin". Please adapt as necessary.
2. On the admin interface, go to /setup/ini settings, select image.ini and the admin siteaccess from list. You should see the following:
3. Create/edit an article, go to "body" field and click on the "Insert / edit image" icon.
4. Search or browse for existing images. The returned images will be disabled, making image selection impossible.
Note: uploading new images will work, though.