Can a Pokeball be used for things other than storing pokemon?
Like a "Hoi-Poi Capsules" from Dragon Ball or even to imprison humans?
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They were made for storing pokémon, only. It can be seen, that some trainers play with them (at least in the games, there are jugglers and some psychics who make the balls float in the air). It can happen, that there are different things than a Pokémon in it, like when Ash found a riceball (?) in his Pokéball after the tries to catch a Mankey, which throws the riceball at the Pokéball, but besides from that, Pokéballs aren't used for anything else than catching and storing Pokémon.
In the anime, it was also shown that a Pokéball can't catch trainers, the beam that would transform the Pokémon to energy (to store it in the ball) just doesn't have any effect.
In the games, however, items which can be found in the world are shown as a red Pokéball. Whether it's for the sake of simplicity or whether they are really stored in Pokéballs is unclear (but you don't get a Pokéball with every item you find).
In the game Pokémon Legends: Arceus, Professor Laventon says at the beginning that the development of the Poké Ball revolves around the idea that every Pokémon is capable of making itself small (which may be referring to the move Minimize), and so the Poké Ball takes advantage of this to shrink the Pokémon and store it inside.
In an early page of the Adventure manga, it can clearly be seen that Nidorino is shrunk inside the Poké Ball, following the logic of the first games that the authors understood.
Following that game material, canonically the Poké Ball is used only for the sake of minimizing and capturing Pokémon. (It's important to note that due to the Arceus game clarifying that use of the Poké Ball, many have been saying that the anime didn't follow that at all, mainly due to the rice-ball catching Poké Ball in the anime.)