Picamerge (U.S. $0.99 on sale) is a rather unique photo app for iOS that is designed solely to create double exposures to make some unique looking images. Gee, in the old days when we had double exposures with a film camera, it was usually by accident!
Picamerge lets you use photos from your camera roll and albums, or you can take pictures using the apps built-in camera functionality. When you have your double image, a slider bar across the bottom lets you adjust the blend, and filters along the bottom of the screen let you try some preset unique looks. The filters vary the transparency of the images, and can add some color effects if desired.
Getting a worthwhile double exposure can take some planning, and it's not the kind of effect you will use very often, but it's great to have when you want it. I can foresee creating some very nice holiday photo cards with a snow effect or candle overlay.
Once your image creation is completed, your masterpiece can be saved back to your iOS device or shared via Instagram, Facebook or Twitter.
Picamerge is just one of those little apps that are worth having when you need them. It is very simple to use, and whether the effect works or not is up to you, and not the app.
Picamerge requires iOS 7.0 or greater. It's universal so iPads, iPod touches, and of course iPhones are welcome. The app is optimized for the iPhone 5.