How to add image gallery to multiple posts

Hello there,

I have uploaded several posts to my site via CSV Importer. However I want to add an additional photo to my posts (two photos total) showing the products. The custom tag that works with my them is image_thumb. That is the posts custom field I have already added to the main image. However, I cannot get the slug for my second image to work with CSV Importer?

So I’m wondering if there’s another way to go about it? Is there a way to attach an image to multiple posts?

I hope that makes sense. My site is here: State Inspired T-Shirt Designs | ActiveState Designs