1. A projection device, which is configured to project an image which is co-operable with images projected by one or more other projection devices, wherein the projection device comprises: a detector operable to detect characteristics of images projected on a display surface by the projection device and one or more other projection devices, and a controller operable to adjust the projection device and to adjust one or more of the other projection devices, based on the characteristics of the images detected by the detector, such that the images projected by each projection device co-operate on the display surface, by overlapping or aligning.