[ChuckMcM]

If its an image it suggests that it might be fun to print QR codes on your mail which refer to specific URLs. If the URL is accessed you get a hit on who looked it up. Sort of like putting a 1x1 gif in an email which is loaded from your web site as cheap analytics (pro tip, don't do this if you work at Google, the security guys don't like it :-).

Always interesting if you can get the other side to reveal information by playing on the fact that they are trying to get as much information about you as possible.

[jack-r-abbit]

That assumes that what ever is getting the images is also going to process them as QR codes and follow any URL encoded in them. Based on what the system is described as doing, I don't see why it would have any concern over a QR code since QR codes are not an accepted form of addressing a envelope.

[ChuckMcM]

All US mail gets a delivery bar code imprinted on it when it is sorted. There are quality checks that verify that the delivery bar code is accurate. Electronic postage is also created using 2D barcodes. My guess is that the folks who build such systems have them just eat bar codes for lunch (which is to say interpret all bar codes) and include that interpretation in the meta data.

If as you say they are never looked at (and I can certainly believe that is true) then the URL you encoded would never be accessed. If however you got a web log entry on your web server that your URL was fetched from a machine run by Booz Hamilton, well there ya go, a bit of information extracted by putting a puzzle in front of them. :-)