look at http://www.zenphoto.org/trac/wiki/ZenphotoHacks#zenphotoasaplug-in for how to use zenphoto outside its realm. Look at the stopdesign theme's index.php file for how to get the latest images.
there should be a slash in the line
require_once(WEBPATH . "" . ZENFOLDER . "/template-functions.php");
require_once(WEBPATH . "/" . ZENFOLDER . "/template-functions.php");
The WEBPATH define should match the folder where zenphoto is installed. I.e. if your zenphoto php files are in photos/zp-core/ then the define would be define('WEBPATH', 'photos');
Anyway, the page you show seems only to be defining the function printlatestimages() which you don't need to (and are not allowed to) do.
Please look at the WIKI description for use of zenphoto as a plugin.http://www.zenphoto.org/trac/wiki/ZenphotoHacks#zenphotoasaplug-in
Follow this example to edit your php page that you want to display zenphoto images. Place the call on printlatestimages() where you want the images to appear on your web page.
For a full example of an index.php page that displays a random image:
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Test Index