Duplicate and near-duplicate digital image matching is beneficial for image search in terms of collection management, digital content protection, and search efficiency. In this paper, we introduce SICO, a novel system for near-duplicate image detection during web search. It accurately detects nearduplicates in the answers returned by commercial image search engines in real-time. We show that SICO — which utilizes PCA-SIFT local descriptors and adapts near-duplicate text document detection techniques — is both effective and efficient. On a standard desktop personal computer, SICO identifies clusters of near-duplicate images with 93% accuracy in under 30 seconds, for an average of 622 returned images for each query.