Setting up those cameras would be illegal where I live.

Whereabouts is that? I hear many people make those claims, but almost as many turn out to be wrong when investigating more closely.

Portugal.

To set up such cameras, you'd need permission from our National Data Protection Commission and if you were to store footage with car plates you'd fall under the Personal Data Protection Law which requires you to either get explicit consent or fall under one of the few exceptions in the law (and no, tracking random people isn't one of them).

And even if you qualify, you can only use that data for the specific purpose you said you needed it for and it needs to be well protected (for example, a governmental CCTV installation was suspended because the recording weren't being well encrypted).