1. A computer-implemented method comprising the steps of: updating a scene model used for object detection in an image sequence by modifying a relationship between a first mode model associated with a first visual element and a second mode model associated with a second visual element, said updating comprising: determining a co-occurrence between the first mode model and the second mode model; modifying the relationship between the first mode model and the second mode model, dependent upon the determination of the co-occurrence between the first mode model and the second mode model; and updating the scene model based on the modified relationship between the first mode model and the second mode model.