Visual cryptography, proposed by Naor and Shamir in 1995, is a scheme which decodes messages by using human visual sensitivity. Cheating has been proved to be possible in visual cryptography. We propose a cheating prevention scheme which precludes members of a group from collusive cheating by using additional images for verification. In each pair of shared images, we detect cheating by mutually verification. The result of verification is clear and directly perceived by the senses. It is a practical technique using authenticating images while the structure of the secret is complex.