This paper reports a study designed to investigate the requirements of a user interface for a content-based image retrieval system, and presents the preliminary results of an inquiry into the usability of the query by visual example paradigm. Twenty eight evaluation sessions were conducted to test the usability of two user interfaces. The study was segmented by image type, user group and use function. Usability was measured using a combination of both objective and subjective measuring instruments: benchmark tasks, critical incidents, and the Questionnaire for User Interface Satisfaction (QUIS). Preliminary findings suggest that both user interfaces had an overall positive usability score, although there were a number of areas that would improve the overall score. The results also indicate that the efficacy of some currently used features are questionable.