Help with PostImage plugin

Hi, I’m trying to figure out how to use the WordPress plugin PostImage: https://guff.szub.net/2006/02/09/post-image/

I have assinged a class to an image in a post, but I can’t figure out how I’m supposed to write the php code for the loop so it uses the class.

I’ve gone through the instructions on the page a few times, but it just escapes me.

Can anyone help?