For some unknown reason, SMF does not display attached images to Guests. When you log in, SMF does display the images. This appears to be a bug, because the settings for displaying images for Guests have been turned on.
If you are reading a page and can't see the REPLY button, chances are about 99.99% that you are not logged in. You must be logged in to post replies or new messages and, as we now know, to see attached images!