According to CBP official policy 41C.F.R.102-74.420 (Title 41 CFR 102-74_public) no photographs or video recording of any type is permitted of CBP personnel performing a job function without prior notification to CBP.
There has been some focus around this issue lately as an increasing number of carriers, in the interest of safety monitoring, are equipping trucks with dash cams. Please consider notifying all cross-border drivers to turn off their dash cams before pulling up to the primary inspection booth at the border.
The cameras can be turned on again once the driver has safely cleared both primary and secondary processing.