From the Super Mario Wiki
In The Adventures of Super Mario Bros. 3 episode "Oh, Brother!", Kooky used the Koopascope to spy on Mario and Luigi in the Mushroom Kingdom from an underground dungeon. By simply inserting the Koopascope into a Warp Pipe, Kooky was able to monitor Mario and Luigi on the other end of a network of pipes.
The Koopascope was clearly designed for capturing purposes, as one can view their target through the Koopascope with crosshairs.