How to reuse a phpThumb thumbnail in Evo

Hello,

I am using Evo 1.0.12 with phpThumb 1.1.

Say you use phpThumb to create a thumbnail for an image TV that is attached to a page.

Once a thumbnail has previously been created by phpThumb, is it possible to reuse that generated thumbnail for future visits to the page (unless changes are made to the image or in the phpThumb call) - or does a new thumbnail have to be created by phpThumb every time someone visits that page?

Eg Is it possible to save and reuse a thumbnail that phpThumb creates (eg to speed up page loading)?

In the phpThumb info on this page: http://phpthumb.sourceforge.net/demo/docs/phpthumb.readme.txt, reference is made to md5s...

md5s = MD5 hash of the source image -- if this parameter is
passed with the hash of the source image then the
source image is not checked for existance or
modification and the cached file is used (if
available). If 'md5s' is passed an empty string then
phpThumb.php dies and outputs the correct MD5 hash
value. This parameter is the single-file equivalent
of 'cache_source_filemtime_ignore_*' configuration
paramters

It sounds like perhaps that is the way to specify use of a previously cached file if it exists. If so, what value do you include with md5s in the options (eg md5s=???)

This is my current call:

Thanks in advance.