1. A toy construction system comprising toy construction elements, the toy construction elements comprising coupling means for releasably interconnecting the toy construction elements, the toy construction system comprising one or more marker construction elements comprising such coupling means and each having a visual appearance recognisable by an image processing means, and a data processing system comprising image capturing means, image processing means, and display means, wherein the data processing system is adapted to capture an image of a toy construction model constructed from the toy construction elements; process the captured image to detect at least a presence of at least one of the marker construction elements within the captured image; responsive to the detected marker construction element generate a computer-generated image; and to augment or replace the captured image with the generated computer-generated image.