This is exactly postcard sized, it is made from a purple Liberty and a yellow Selfridges plastic shopping bag, with pieces cut to more or less the right size then ironed/ fused together using an iron between two layers of baking parchment and then I've free-machined (feed dogs down and darning foot on) the stitching, with a layer of Stitch'n'tear on the back (just to make sure it's stable). Here's a pic of the back:
And despite my best intentions, it's still not been stuck onto a postcard... But will be eventually.
If you want to know more about this sort of sewing technique - Gwen Hedley's book Surfaces for Stitch: Plastics, Films & Fabric is a really good book with some projects but mostly techniques so you can find out how to do it, then apply it to what you've got. Gwen teaches textiles in the UK, and probably overseas too.
I did a course with her at Missenden Abbey to learn the skills to do this for one of my City & Guilds Embroidery finished pieces. It's based on skeletons, and I'm still not convinced by it... Still mum likes it and has it up in her house, I think it probably needs framing (and the top droops which needs sorting out). Anyway, I love the surfaces you get with sewing on fused plastic.