Where do I edit output code to mark-up an image url?

Question

Hello,

I have a wordpress site with these two image gallery plugins:

http://wordpress.org/extend/plugins/nextgen-gallery/

http://wordpress.org/extend/plugins/nextgen-smooth-gallery/

I want to add some extra markup(for a resizer php) to the image urls, but can't find where in the plugin code to do it. What should I be looking for?

Your help would be so appreciated!

Thanks, zeemy