The algorithm described by Heike is essentially just looking for striped red and white shirts. Anyone who's done more than a couple of "Where's Waldo?" games knows that striped shirts are often thrown in to draw one's eye. In fact, in this very example there is another striped shirt (lower left corner, just above the wall) which could very well have been Waldo that this algorithm did not highlight. Without being able to recognize Waldo's human characteristics (thin, glasses, strong chin) the approach described will inevitably fail.