License Plate Cameras for Vehicle Monitoring

One of the most productive applications for security cameras is the use as a vehicle “License Plate Recorder”. This use is consistent with one of the basic principles of visual surveillance: monitor choke points. Gated communities, hotels, parking lots, private estates, and critical infrastructure are all logical markets for license plate recorders. The benefits of this practice include improved security. Upscale businesses also find that they can better serve repeat customers. At, for example, a restaurant’s valet parking area, when Mr. and Mrs. Jones arrive, the system can alert the staff so that they can be greeted personally, and their service can be tailored to their particular needs. More sophisticated systems can automatically read the license plate from a graphic to a text signal (Automatic Character Recognition). This allows automated checks against known lists.

All license plates in North America are 12 inches wide and 6 inches in height (300 mm X 150 mm). Lettering heights vary somewhat, with 2.5 inch lettering the most common. Different states use different combination of letter and number groupings. The requirement of a license plate light has been the law in most states for more than 50 years. 19 States do not currently require a front license plate, and in our current economic environment, this number is likely to grow as states try to reduce cost (each plate cost a little more than $1 to produce).

The location of the recording camera will be dependent on the:

• Chosen point of monitoring,
• Mounting location, and
• Access to facilities including electricity

The chosen point of monitoring will usually be the entrance or exit (or both) to the area. An ideal location will cause the vehicle to slow, improving the photography, but good quality can be obtained with conventional equipment for vehicles traveling at less than 40 MPH. This slowing mechanism can be a guard arm, a speed bump, or a sharp turn. It is feasible to record the license plate of a fast moving vehicle, but it is more complicated, hence the equipment is more expensive. The width of the traffic lane can complicate the job. A narrow lane reduces the variability of the vehicle and license plate location.

The mounting location will depend on the situation. If the environment is prone to vandalism, mounting the camera out of reach, and/or housing the camera in a vandal resistant enclosure, will reduce the vulnerability. A camera can be installed remote from the chosen point of monitoring by 150-200 feet. The use of a lens can compensate easily. The viewing angle, both horizontal and vertical, from the camera to the automobile should be less than 40 degrees. Larger angles distort the view and make recognition more difficult.

Access to facilities is an important consideration. With current technology, it is possible to install a security camera without any umbilical lines. Power can be supplied by solar energy, and the video signal can be transmitted via RF signal (radio). However, if possible, keep it simple. Solar panels and RF Transmitters capable of video transmission can be expensive.

A final consideration is video storage. This hardware can be equipped locally, or a coaxial cable can be installed. If frequent review of the imagery is anticipated, the storage should be located in an accessible location, either physically or via a network. Most modern video storage systems (DVR, digital video recorder) are compatible with both LAN and Internet network protocols

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