Okay, just went over to snapfish and had a look.
1)Click on the album you want to share from.
2)Click on the picture you want to share.
3)On the right there is a bar down the side with options, click share photo.
4)Above your photo are tabs, click "get a link."
5)Copy the link.
6)In your post type (no spaces though) [ img] paste your link then [/img]
Honestly, that's a lot of work and you may be better off uploading your pics to photo bucket or flikr and then all you'd have to do is copy and paste the links into your reply. It might be a pain to make new albums but it would be much faster in the end.