Apple's wallpaper adjustments for iOS leave something to be desired. You can't rotate the image, and if you try to scale it, the image often snaps back, making a mess of your intentions.
Fix and Set Wallpaper (U.S. $0.99) is a simple app that fixes Apple's shortcomings. You can pinch, rotate, crop and position a photo however you want. You can preview the wallpaper on your home screen. If you use a photo zoomed out, the app adds a black border to your image. When done, you can save the photo to your library, then set it as wallpaper using Apple's tool. There is also an option to share your new wallpaper via email or iMessage.