Fingerprinting schemes use digital watermarks to determine originators of unauthorized/pirated copies. Multiple users may collude and collectively escape identification by creating an average or median of their individually watermarked copies. We present a codebook generation scheme to enhance the Anti-Collusion fingerprinting (AND-ACC) scheme to make it scalable for supporting large number of users. We evaluated our proposed codebook generation scheme using HVS based watermarking scheme and our own fingerprints. The simulation results with standard test images show good collusion detection performance over average and median collusion attacks.