1. Change detection apparatus for detection of changes between first and second stereoscopic image pairs obtained at different times of a substantially similar view, the apparatus comprising: a two-dimensional image filter for comparing said first and second image pairs to obtain an initial list of change candidates from two-dimensional information in said image pairs, and a three-dimensional image filter for comparing at least one of said first and second image pairs at said change candidates using three-dimensional image information in said image pairs to retain change candidates correlating with three-dimensional image information and to reject change candidates not correlating with three-dimensional image information, thereby to produce a refined list of change candidates.