We already looked at using PHP to resize images on the fly, but using the same technique to create image thumbnails has problems. At the very least you will want to save time by storing the thumbnails as they are generated to avoid major slow-down. Perhaps the easiest way to implement this is to count the number of files in your images directory, compare it against the number that were there the last time the script was run, and if the number is different then regenerate the thumbnails.
Copyright 2012 Future Publishing Limited (company
registered number 2008885), a company registered
in England and Wales whose registered office is at