In a computer processing apparatus 8, frames of image data received from a camera 4 are processed to track the eyes of a user 2 in each image. A 3D computer model of a head is stored, and search regions are defined in the 3D space corresponding to the eyes and eyebrows. For each image, pixels within the projection of the search regions from the 3D space to the 2D image space are sampled to determine a representative intensity value for each of the search regions. Positions for the eyes in the 3D space are then calculated based on the determined values. The 3D computer model and search bands are moved within the 3D space to align the eyes with the calculated eye positions. In this way, when the next image is processed, the search bands project into the image from a head configuration determined from the previous image. This facilitates reliable and accurate eye tracking.