There isn't currently an explicit no-cache setting. You have two options:
1.) Set up some kind of scheduled task to delete image files older than a particular date. This way, you still have the benefits of caching but you don't keep absolutely everything that has ever been accessed. I haven't really done this under Windows before, but a quick Google search turned up this project, which might help: http://code.google.com/p/autologcleanup/ . I'm sure there are many similar tools if you hunt around a bit.
2.) Modify web/bookcover.php to disable caching. It's very easy: there's a function called processImageURL() which takes a parameter that controls caching on a service-by-service basis. If you simply add a new line to the very top of the function:
$cache = false;
then no images will be cached.
I'd personally recommend option #1 -- that's the reason this isn't currently a configurable setting -- but option #2 should work too.
From: Harris, Gary [firstname.lastname@example.org]
Sent: Thursday, April 26, 2012 4:59 PM
Subject: [VuFind-General] Cover Images
Is there a setting on VuFind that tells the system not to save copies off the cover images? Whenever I WinGrep the system for certain strings, it takes forever because grep has to search through about 20,000 cover images.