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Newspaper “spot the ball” competitions are always popular. The ball is airbrushed out of a sports picture and a prize is offered for the best guess on where it should be. British inventors William Constantine and Steen Cartwright have now added a neat twist (WO 03/89083). At least two pictures are taken, either from different positions round the pitch, or at slightly different times. The ball is then removed from one picture, forcing contestants to use their trajectory-prediction skills, or work out the difference in perspective between views from different angles.