Five leading Internet service providers will jointly build a database of child-pornography images and develop other tools to help network operators and law enforcement better prevent distribution of the images. The companies are set to pledge a total of $1 million today to form a technology coalition as part of the National Center for Missing and Exploited Children…The participating companies are Time Warner Inc.'s AOL, Yahoo Inc., Microsoft Corp., EarthLink Inc. and United Online Inc., the company behind NetZero and Juno…Plans call for the missing children's center to collect known child-porn images and create a unique mathematical signature for each one based on a common formula. Each participating company would scan images sent by its users for matches.