Keyword spotting is also defined as a separate, but related, problem in the context of document image processing.
In the United States, the National Security Agency has made use of keyword spotting since at least 2006.
[3] This technology allows analysts to search through large volumes of recorded conversations and isolate mentions of suspicious keywords.
Recordings can be indexed and analysts can run queries over the database to find conversations of interest.
Given a query, the goal is to retrieve the most relevant instances of words in a collection of scanned documents.