Do you mean, capture the image only after a warrant is issued?

That doesn't seem realistic: Almost all the time, we only know about a crime after it happens - when it's too late to obtain a warrant. We get the license plate from the video of the crime.

So I would capture the images, minimize and encrypt it at the point of capture (before storage or transmission), and maybe even setup some PKI where only judges can issue keys to decrypt, if practical.