[adiabatichottub]

Who needs a whole blockchain? Just basic public-key cryptography would do the job.

Imagine if you will, that the NVR (recording system) has a unique private key flashed in during manufacturing, with the corresponding public key printed on it's nameplate. The device can sign a video clip and its related meta-data before exporting. Now, any decent hacker could see possible holes in this system, but it could be made tamper-resistant enough that any non-expert wouldn't be able to fabricate a signed video. Then the evidence becomes the signed video and the NVR's serial number and public key. Not perfect, but probably good enough.

[hippari2]

Unfortunately consumer devices often have weak cryptography built into them. The one properly implemented are just out of reach for average consumer.