A team of the Department of Informatics of the Aristotle University of Thessaloniki consisting of PhD student Eleftherios Spyromitros-Xioufis, postgraduate student Konstantinos Sechidis, Lecturer Grigorios Tsoumakas and Professor Ioannis Vlahavas took the 1st place at the “concept-based retrieval” subtask of the “photo annotation” task of the ImageCLEF 2011 challenge. This challenge was part of the International Conference on Multilingual and Multimodal Information Access Evaluation (CLEF) 2011.