All your 10 postcards should be original artwork!
Art is about making something new that did not exist before, or transforming it to something that is yours.
Original means that you do not send out photocopies, but to duplicate your own style or to repeat a motif that you love, and make similar postcards is totally okay. Its also fine to make all of them different. I love working with a theme, so that you can tell that all ten postcards belong to the same “series” but they are all slightly different and of course, originals.
You are the artist. Make it fun for you!
This page is part of the Postcard Swap FAQ