Sadly, number places can be seen whenever your car is on the road. It'd also be easy for someone to see a random number plate, add 1 to it, look up the details in carjam.co.nz, then have the details for a different car. Like this one, which is an 'off by one' for my number plate:
https://www.carjam.co.nz/car/?plate=XA4555
So I don't particularly care if my number place is online. However, some people do care - and I appreciate the effort photo takers take when they remove the number plates from their photos.