CELI Participation at ImageCLEF 2006: Comparison with the Ad-hoc Track

In this paper we discuss the CELI’s first year of activity at CLEF in the context of Cross Language Image Retrieval Track (ImageCLEF). The proposed system is an upgrade of CELI’s cross language delegated search system (www.elois.biz). The system is meant to perform CLIR on the web by using Google and Yahoo indexes. Therefore the goal is to provide reasonable translations of queries with no direct access to the corpus. This, in turn, means absence of tuning procedure for the system and impossibility to impose restrictions in terms of domain, style, etc. Our approach is based on bilingual dictionaries and the main research effort was devoted to filter out the noise introduced by translation ambiguities. We experimented a disambiguation strategy based on Latent Semantic Analysis which allow us to compute the degree of semantic coherence of possible translation candidates. We also tested some query expansion methods in order to “balance” the fact that the system does not perform any kind of visual retrieval. Being the system basically the same, we are in a good position to compare results in the Image track with the one in the Ad-hoc track. Surprisingly it emerges that, contrary to what happened in the Ad-hoc exercise, expansion strategies improve results in image retrieval tasks.