Deco Sketch Pro is a universal iOS app that features geometric effects that can be added to images you have, or you can start from scratch. The US$2.99 universal app includes 10 brush types with 130 variations. You can extract color from a photo and use it as the base for an effect. You can start with a blank page and create your own designs, useful for creating desktops or other graphic art.
The app is simple to use, and when you first load it, you get some help in identifying the on-screen icons. From there, I found it's just a matter of exploring. With photos, you can add things such as sunbursts or other shapes -- whatever you can dream up. It's powerful as a painting tool as well, and while I am no artist, I was able to create some interesting designs that would have been difficult to create with other drawing for painting programs.
Controls allow you to zoom so you can work in detail on your image, and unlimited undos let you can fix anything that went wrong. The app worked smoothly on my iPad as well as my iPhone 5.
When you are done creating, the app lets you output 8 MB images (2,448 x 3,264), which matches the iPhone 5 camera resolution. The app lets you share your creations to Facebook, Twitter and email. It's a bit hard to describe the compelling output from this app, but check the gallery for some samples.