1) From any chat (one-on-one or group), tap the Settings icon in the upper right corner. 2) Tap on ‘Set Background’. 3) Choose from the image gallery that’s optimized as background for your chats. 4) You can also use your own photos by tapping ’Choose Photo’, and select from an album or open camera to take a picture. 5) Background only applies to the specific chat you set it for. You can customize each chat!