A distributed computer system comprises a first computer and a second computer. The system is arranged for a digital image to be transmitted from the first computer to the second computer, via a telecommunications link, as plurality of co-ordinates defining, in three-dimensional space, the vertices of a plurality of polygonal surface facets of the image. The second computer is arranged to enhance the image by modifying the image according to the co-ordinates of said vertices. Only a small amount of data need therefore be transmitted from the first computer to the second computer for a high resolution image to be displayed by the latter.