iOS 8 added recent contacts to the app switcher (double tap the home button to bring up app switcher) in the form of their pictures in circles. If you don't like the looks of this, or just don't use it for access to your recent contacts, you can easily shut it off. Go to Settings -> Mail, Contacts, Calendar and scroll down to Show in App Switcher. Tap on it and toggle off Recents.
How do I get rid of Contact's pictures in my iPad's App Switcher?
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