I like the barcode idea because they have to scan it, proving that they were actually on the correct premises. Without that, what's to stop them from dumping it at any neighbours residence (as especially Fastway are wont to do), or just never attempting to deliver it at all, and then just using the leave authorisation to escape any responsibility? I'm not concerned about goods being stolen post-delivery, just about them being delivered in the first place. I guess if I have surveillance on the specified leave area, then a missing 'delivered' parcel that was never present in that area can only be their problem.
Barcode is a bit lame, they could easily take a photo of it and scan it whenever. I would prefer a NFC based tag, with the scanner also doing geologging of it and sending it back to a web interface, with me getting a push notification when something is left there.
We went to ATL with courier post because their driver for our neighbourhood used to leave ca ard without even knocking. I watched the lazy bugger do it one Saturday. I happened to be on the roof when he crept up the stairs like a cat burglar with the pre-completed card and no parcel, put the card down and crept off again. It was comical to watch. He nearly soiled himself when I yelled out "Oi! where is my parcel!" from the roof.
If you have a natter with your regular driver they may be happy to start zapping something if they know you are geek savvy and have the ability to do so.
Depending on the scanner they use, some require signature regardless (sometimes signed by the courier or simply atl etc) along with an entered first name to help decipher it
Believe Courierpost/NZ parcelpost zap a barcode when they collect bags from post shops and mail drop boxes, to make sure the clearing times are kept to (to make sure they are not beating the system and peeving late droppers off)
If they find it will be easier than filling out the screen themselves saving a second or 2 they may well love it, could then make one in Code39 with your address or name and a keyword and rotate it weekly/daily. As savvy drivers of course will be able to use a standard reader and duplicate it, but I'm not sure they would bother if it was just... there.