x11vnc has an experimental and somewhat brute-force implementation of client-side caching. It is enabled via the -ncache option. When creating the RFB frame buffer in this mode, x11vnc allocates a very large scratch region below the top portion used for the actual (on-screen) pixel data. x11vnc can then use the RFB CopyRect command to instruct the viewer to move rectangles of pixel data into and out of the scratch region. These moves are done locally on the viewer side. In this way x11vnc can manage the scratch region to store and retrieve pixel data without having to resend it over the network.