Online camera calibration methods have been proposed whereby calibration information is extracted from the images that the system captures during normal operation and is used to continually update system parameters. However, such existing methods do not cope well with structure-poor scenes having little texture and/or 3D structure such as in a home or office environment. By considering camera families (a set of cameras that are manufactured at least partially in a common manner) it is possible to provide calibration methods which are suitable for use with structure-poor scenes. A prior distribution of camera parameters for a family of cameras is estimated and used to obtain accurate calibration results for individual cameras of the camera family even where the calibration is carried out online, in an environment which is structure-poor.