Hi Graham
Problem with pictures outside is did they actually get left there, did some one come along later or did the customer get them and not say. Its really a bean counting exercise, it will be dependant on your product price, and your assumption of how many are going to try it on - compared with the cost of the signature on every parcel.
Signature is always the best for the reasons you highlighted.
To share the recent experience we had when we switched to 2D on normal 2nd class small parcels. We did not get them many, but the issues dropped by 90-95%, we put it down to them seeing the postman scanning the barcode or them seeing the barcode. We still get the Smart Alecs who try it on, but the the reduction was huge and it cost nothing.
May be worth setting a £ limit for orders so that fulfilment house can trigger a signature at a certain level, so if the order is >=£10 etc then send it signed for.
Is there any reason you are going tracked 48, do you really need to see where it is, its been?
Small Parcel with signed will be a little cheaper, and you can get the security of the signature.
Forgot to mention we found the 2D parcels also get delivered faster, so the 2-5 day it was taking, turned in to most be delivered in 2 days, and 3 days the exception rather than the rule.
If you need anything else don't hesitate.
Regards
Alan