Same images used twice but differently

I got some nice pictures that I put into a layout with medium sized thumbnails, that get enlarged when you click on them - one by one. It works well and I like it. Now somebody in our group asked me, if I could make a gallery with these pictures, which of course I can easily do (thank you Sparkle).
My question is: Can I use the same pictures again, or do I have to import them again for the Gallery. If that is possible, how can I find them integrated in the Sparkle file?

You need to add them again.

Thanks Duncan for the fast reply.