A system and method for three level authentication of a user has been disclosed. The system 100 performs three level authentication: first level being selection of at least one predefined image from a plurality of images including decoy images; second level being selection of at least one predefined tile in the tiled version of the selected images to generate a transaction key; and the third level being entering a transaction key generated after first and second level are successfully completed, which is used for final account login and grant of transaction rights. The authentication is done on user's computing node 110 by communicating with authentication server 102 for first and second level authentication and the transaction key for third level authentication being generated by transaction key generating server 124 and transmitted on to user's computing node.