Naumann, A.B.A.B.NaumannFranke, T.T.FrankeBauckhage, ChristianChristianBauckhage2022-03-112022-03-112009https://publica.fraunhofer.de/handle/publica/36256510.1007/978-3-642-03658-3_79en005006629400Investigating CAPTCHAs based on visual phenomenaconference paper