"Why not take advantage of the mobile device itself?  Since most smartphones are equipped with both accelerometers and cameras, if it detects the individual is walking while using a messaging application, it shouldn't be hard to program the device to engage its camera to project what is on the other side of the phone onto the messaging app's screen background.  When the user isn't walking while interacting with the device, it could switch to a more opaque background, improving its functionality.  "