Matt's Random Image

Hi,
I am integrating Matt’s Random Image script into a sidebar widget
https://ma.tt/scripts/randomimage/

It works except that it only randomizes on page refresh and not when I simply go to another page. I have to actually click the refresh button in the browser for it to randomly choose another image. I assume it has something to do with caching?
Is there any way to have it randomize whenever you go to a different page?
Thanks.