making the optimal target for SIFT

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I'm working on tracking a doughnut shaped target with SIFT as the detector. I just drew this target with a marker and then cut it out with scissors. It works okay but I keep wondering if there's a better pattern I could come up with?

And I know it's a bit dark, but I took this picture with my device's camera. I did try equalizing the histograms of both the target and the incoming image, but it only made a little difference.

Thanks!