right now, neither needs a warrant. if searching LPR camera history starts to require a warrant, it probably wouldn't take much to argue that sending officers out to manually do the same thing should require one too.

EDIT: i have no doubt that Flock and other ALPRs got so widespread because four ALPRs watching each direction at an intersection is basically invisible in comparison to four cop cars at every intersection.

if plate readers were as visible as cop cars (including agency branding) people would have probably gotten bent out of shape a long time ago.

On a recent 3k mile cross-country trip I was shocked to see how prevalent Flock cameras were, even in tiny back-woods locations. I'm fairly certain you cannot drive long distances in the US anymore without Flock having a detailed record of your travels.