Thirding my own opinion :)

I would mention to the customer that the Gun Type is well known, reliable, and adds ZERO risk and almost Zero programming cost.

Using the device camera... is a risky science experiment that will probably burn a lot of time and money and may or may not work well - it WILL NOT save money.
( I have done enough "science experiment" projects to recognize this kind of money-pit when I see it. Not saying it can't work, just MUCH riskier than the customer believes. )

Get a gun type that does keyboard emulation, no special interface, no DLL, no .NET and best of all: no worries!

Cheap too:
https://www.barcodewarehouse.biz/eCat/handheld_scanners/cipherlab_scanners/pos_usb_scanners/1500_1d_scanner_black_usb_cable.aspx