Described are systems and methods for screen sharing between computing systems. A guest system and a host system are coupled to a server over a network. The guest system automatically executes program code embedded in a web page received from the server. The program code sends a request to the server for image data corresponding to an image on a display screen of the host system. The host system automatically executes program code embedded in a web page received from the server. The program code captures image data from the display screen of the host system and sends the captured image data to the server. The server sends captured image data received from the host system to the guest system in response to the request from the guest system. The guest and host systems can participate in a screen-sharing session without having to download and install special software.