To do this, you need to include the global config variables and the functions. Where are you trying to add the random images in relation to the plogger installation? For example, I need to know if you have your plogger installation at http://www.pandianbe.com/plogger/ and you're including the random images on http://www.pandianbe.com/random.php.
If you let me know how your website is structured, I can help you with the necessary code.