Various embodiments process updates of an image transmitted between a first terminal and second terminal for screen sharing, wherein updates to the image at the first terminal are also displayed at the second terminal. The image is divided into an array of contiguous sub-tiles, each sub-tile comprising more than one picture element of the image. When a plurality of sub-tiles of the image have changed at the first terminal, at least one of said changed sub-tiles and at least one contiguous sub-tile are selected to form a tile. The tile is encoded for transmission to the second terminal, and includes sub-tile data identifying which sub-tiles are included in the tile to enable updating the image at the second terminal in accordance with the changes to said changed sub-tiles. The configuration of the tile is flexible such that the number of contiguous sub-tiles encoded in the tile can be varied.