"backup camera", no hyphen or space, is at least popular enough to have a wikipedia entry.

https://en.wikipedia.org/wiki/Backup_camera

it is also used very regularly elsewhere, like government sites: https://www.nhtsa.gov/vehicle-safety/driver-assistance-techn...

or legal advice sites: https://thelegalguide.org/are-backup-cameras-required-all-ca...

or news sites: https://abcnews.com/US/cars-us-now-required-backup-cameras/s... https://www.reuters.com/article/business/consumer-groups-sue...

or automotive magazines: https://www.autoweek.com/news/a1892066/feds-backup-cameras-a... https://www.caranddriver.com/car-accessories/g44411856/best-...

it's safe to say that "backup camera" is perfectly acceptable.