Maybe make this a blockchain project instead. Videos of cops doing bad things should be decentralized, non-deletable, and optionally anonymous.
There is no algorithm for truth, so in practice you need a way of allowing groups to form consensus about the validity of claims relating to pieces of data in the system. A claim might be "The image with hash ABC123 is a deepfake."
It might be possible to layer a system with that amount of nuance on top of a blockchain, but you need to be really careful that your system won't end up making the world much worse before it has a chance of making it better.
If you know that a specific cop is going to be at a specific location at a specific time, you could create the deepfake in advance and add it to the blockchain when they show up.