Where would one place such a message if they wanted it to show up just above the "Add a comment" text? I don't think it is inherently obvious that there is a nice big original picture hiding behind the one you get when you click on the thumbnail.

In the "/zenphoto/themes/default/" directory (or whichever theme you are using) place this line:

Click For Larger Image

Right above this line

``

Perfect! That worked great. Thanks for the quick reply and sorry for the late response (been out of town).