difference between a keyboard and a barcode reader

Usually a barcode reader will apply or can be setup to apply a custom 'marker' at the pre- and post- ends of the data.

You can then use this to determine where the data has come from by checking for this marker.

As for identifying the hardware, you would need to know the various hardware ID's for the types of device you want to check for, and you should be able to get those from the OEM.

I dare say if you look hard enough on google, somewhere someone will already have compiled a list of the common ones, after all there are lists of eveything else out there :)