Yes you can share the postcards you get. In fact, I think its great if you do. The swap is about inspiring each other and if you share what you get youll inspire even more people. Each creator has the copyright, but as long youre purpose is not commercial it is okay to share them on instagram (hashtagged #diypostcardswap), in the link up post on my blog, on your own blog or in the Flickr Group!
Please do not share someone elses e-mail or their postal address, in writing or as a photo of the back of the postcard, though. Some people will not feel comfortable having these things floating around online.
All links/resources can be found on the main swap information page.