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These markers are far from ideal for the toolkit. The pattern is off centre which means that, even when cropped as close as possible, a lot of pixels will be the same between markers. This makes it much harder to distinguish between them. The white border around the square area is quite thin which makes it easy for fingertips to break the edge detection mechanism. The non-square nature of the squares doesn't seem to have a large effect on the detection and the slight distortion in the 3D transformation that results could be fixed with an offset in the code. With a good Logitech webcam, I was able to recognise each marker when the markers were layed out on a flat white surface and the camera pointed at them. Unfortunately, holding the markers up to the webcam presents a more complex background and the image is as likely to appear in the user's mouth as on the marker.