Title nit: "backup" means a second copy, "back up" is the verb phrase for moving backwards. Verb phrases get hyphenated for clarity when used as adjectives immediately preceding a noun. So this should be "back-up camera", not "backup camera".

"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.

I think this may be a case of language evolving/devolving and quite possibly an Americanism.

I'm British and to me backup means having a reserve or spare ready to use. You have a battery backup on your servers to step in when there is a mains problem, a photographer will have a backup camera, you backup you files regularly etc.

We would call this a reversing camera, for when you reverse your car using the Reverse gear. You can back into a parking space, or even just back up a little bit into a better spot.

One thing I'm seeing which irritates me is people are starting to call backing singers backup singers. They are not a backup the the lead singer, that would be an understudy, they are supporting like the backing on picture.