Federal law prohibits members of the general public from obtaining other individuals' motor vehicle records except in specific cases. If your use case falls under the exceptions to this federal law, contact your local Department of Motor Vehicles to check a license plate number.
States such as Texas further restrict the disclosure and use of motor vehicle information, including license plate numbers. Checking license plate numbers with the DMV ensures that you are entitled to obtain this information in your state, and that the search is conducted in compliance with all local laws. There is no guarantee that third-party license plate search sites obtain and release license plate information legally.
Select states offer an online license plate lookup for the purposes of checking license plate availability. These searches do not return any personal information about the license plate's owner; they only determine whether or not a plate is in use. The searches are intended for use by individuals who want to purchase vanity license plates.
Department of Motor Vehicles employees who release motor vehicle record information to unauthorized parties face both civil and criminal liability. This liability is to the person whose information is released; the owner of the license plate can sue the releasing employee for monetary damages.