The ads on the backstop -- also at tennis court-side, and other similar places -- have been around for a _long_ time. The technology employed was _commercially_ deployed back in the mid 1960s for U.S. television. known as 'chroma-key', you could use it to drop in a 'replacement' image for anything that was in the scene of a particular color. Usually, the gear was set to trigger on a fairly narrow range of blue. Blue was the commonly-used color because it was not a component of 'flesh tones'.
To make the insert of the replacement image 'believable', the camera that provided the original scene needed to hold a fixed view of that scene. You know "something's funny" when, for example, one part of the image zooms in, while another part _doesn't_.
Note: The original chroma-key technology was pure analog, some early hardware was employing vacuum tubes. It was only a little more complex than the circuitry in the basic 'special effects generator' used for "split-screen" "corner inserts", etc. In fact, it shared most of the circuitry with the special-effects generator.