Image rollover effect when its not a project index page

[mr.wren]

I would like to add an image hover effect (show another image behind) to the thumbnails on this page. But this is not a Project Index as the images are just clickable pdfs and not actual project pages.
https://firstoff.dreamhosters.com/writings/
Thanks for your help!

[arminunruh]

Hey, the image hover add-on only works with texts, not with other images. Sorry :/