With intelligent processing, cameras have great potential to link the real world and the virtual world. We review advances and opportunities for algorithms and applications that retrieve information from large databases using images as queries. For rate-constrained applications, remarkable improvements have been achieved over the course the MPEG-CDVS (Compact Descriptors for Visual Search) standardization. Beyond CDVS lie applications that query video databases with images, while others continually match video frames against image databases. Exploiting the temporal coherence of video for either case can yield large additional gains. We will look at implementations for example applications ranging from text recognition to augmented reality to understand the challenges of building databases for rapid search and scalability, as well as the tradeoffs between processing on a mobile device and in the cloud.