Image Retrieval: Benchmarking Visual Information Indexing and Retrieval Systems. This article was published in 2007 and it has made me curious as to what advancements have been made to image retrieval since that time. It also makes me curious if situations like tagging friends in Facebook photos would be an example of a combination of content and concept indexing. When humans select and tag friends faces Facebook then, I assume, uses that information to compare other photos against the tagged photos and prompts the user to select if the identified person matches the original entered name. I wonder if that software is proprietary or if it simply requires too much human input to be useful.