The wikipediaMM task provides a testbed for the system-oriented evaluation of ad-hoc retrieval from a collection of Wikipedia images. It became a part of the ImageCLEF evaluation campaign in 2008 with the aim of investigating the use of visual and textual sources in combination to improve the retrieval performance. This paper presents an overview over the wikipediaMM 2008 task's resources, topics, assessments, participants' approaches, and main results. Categories and Subject Descriptors H.3 [Information Storage and Retrieval]: H.3.1 Content Analysis and Indexing; H.3.3 Information Search and Retrieval; H.3.4 Systems and Software; H.3.7 Digital Libraries; H.2.3 [Database Managment]: Languages--Query Languages General Terms Measurement, Performance, Experimentation Keywords ImageCLEF, Wikipedia image collection, image retrieval, evaluation