Camera Launcher allows you to easily open your camera app from anywhere by swiping up from the home button (Android 5.1 and earlier) or holding down the home button (Android 6.0+). This replaces the Google Now gesture.
For devices with physical buttons, either holding down or double-pressing the home button will launch Camera Launcher instead.
This app also provides a Camera icon in the app drawer on devices such as the Nexus 7 (2012) that don't show the icon by default.