In order to allow humans to hand draw images with the same function as a QR code, members of MIT Media Lab created 'Graffiti Codes.' Researchers Andrew Lippman and Jeremy Rubin worked to let users encode physical surfaces with data without having to print anything out. Using only a marker or some spray paint, you can draw out a code while Graffiti Codes works to guide you. Currently, the code can only be drawn effectively on flat surfaces.
Instead of using your phone's camera capabilities to scan the code, Graffiti Codes requires that you use the accelerometer. Your phone is able to access the stored data just by tracing over the path. The accelerometer stores a digital image of the path in order to convert it into a link to a webpage.