In an article about generating a color QR code, I described how a mobile phone QR code reader takes an image of a QR code, straightens it up if it is skewed, then drops the image into a grid, somewhat like dropping tiles on a scrabble board. The QR code scanner program evaluates each tile of the grid using an algorithm to make an absolute choice: Is this a light tile or a dark tile? This “light tile / dark tile” information is then used by the program to decode the QR code.
Two important things about the grid: Just like when you play Scrabble, the tile doesn’t have to necessarily need to stay within the lines – the tile just needs to be mostly in the square. Also, the tiles don’t need to be black – and the board doesn’t have to be white. The board could be yellow and the tiles could be blue. This means you can have a QR code grid that has sloppily placed tiles and is a variety of colors, just as long as the algorithm can accurately determine which cells are “mostly” a light color and which are a “mostly” dark color.
Now that you know how a QR code scanner program reads a QR code, you can understand how a colored or hand-drawn or human created QR code can work. I’ve seen dozens of real world examples of QR codes that have been hand drawn, that have been cross stitched, that have been made of food and other natural materials.
Once you have created a readable “black and white” QR code, you can use any image editing program to modify it or you can use tracing paper or an artist’s light box to “trace” the original QR code to make a hand drawn version of it. Because the grid needs to have tiles that are “mostly” dark and “mostly” light, you can stretch the limits a bit when hand drawing a QR code. For example, you can round the edges of the squares or blend the squares with curved lines, or draw light lines anywhere on the code, somewhat like a vine. If you make a mistake, you can use white-out to correct the problem. If your design isn’t too radical, you won’t even need an artist’s light box. You can use a pen and whiteout to draw directly on the original printed QR code. If you draw on the original printed QR code it will be easier to occasionally check it to make sure it is still readable.