I recorded a video of water (from a garden hose) spraying against a piece of clear acrylic. I then
sandblasted the center part of the acrylic with gravel, making little white dents. When I project the video
back onto the acrylic, the video image is only visible where it lands on the sandblasted area.

Spray (video still)
Video projection on sandblasted acrylic, nylon string
Dimensions variable