Armed with my trusty iPad original and a screenfull of arty apps I could not resist, I have decided to try each one out in turn. Some will output images too small for even a postcard, but it will be fun anyway.
This one is made in LetterMpress which is tricky at first but I love the results. Watch out though, it is a great time-eater.
Output was by email, PNG, 1446 x 2048 pixels on the iPad 1. There does seem to be a clear background PNG option, but I haven't found it yet (this was my first try). You can also print, copy, save to photo album or send to Facebook and Tumblr.