우선 좀 detail 한 법률적인 부분을 배제하면
Dashcam 사용 자체로는 불법이 아니나 어디에 장착하느냐에 따라 불법이 될 수 있습니다.
대부분의 주에서 앞 유리에 부착하는 건 불법입니다.
Dashcam 뿐만이 아니라 GPS, Phone mount 등등
https://dashcamerasreviews.com/dashboard-camera-legality-usa/
구체적으로 California만 말씀 드리면
부착하는 장소가 정해져 있습니다.
California Vehicle Code (CVC 26708(b)(13)(A)
(13) (A) A video event recorder with the capability of monitoring driver performance to improve driver safety, which may be mounted in a seven-inch square in the lower corner of the windshield farthest removed from the driver, in a five-inch square in the lower corner of the windshield nearest to the driver and outside of an airbag deployment zone, or in a five-inch square mounted to the center uppermost portion of the interior of the windshield. As used in this section, “video event recorder” means a video recorder that continuously records in a digital loop, recording audio, video, and G-force levels, but saves video only when triggered by an unusual motion or crash or when operated by the driver to monitor driver performance.
http://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=VEH§ionNum=26708.