The Cydia Tweak SwitcherPaper has been officially released and works with devices that have iOS 8 or higher. SwitcherPaper jailbreak tweak lets you to replace the default App Switcher background in iOS 8 with any custom image of their own. The image can be loaded from the Photo Library or you can take a picture on the spot and use it. After you have installed this tweak, you will be able to configure it to your own personal preferences in the Settings app.
If you are interested, then you can download SwitcherPaper iOS 8 from the BigBoss repository in Cydia just $0.99. To install this program requires a jailbroken device (see if and how you can do the jailbreak to your iPhone by clicking here) and you need an Internet connection to download the package. This tweak is compatible with iOS 8.0 and later versions of the mobile operating system from Apple.