A computer-implemented technique can include receiving, at a server computing device having one or more processors, a first video stream from a first user computing device associated with a first user. The first video stream can include a first image portion. The technique can further include extracting the first image portion of the first video stream in order to generate a first overlay stream, and receiving a second video stream from a second user computing device associated with a second user. A composite video stream can be generated from the first overlay stream and the second video stream. The composite video stream can comprise the first overlay stream superimposed over the second video stream. The composite video stream can be output to the second user computing device.