It's been a very long time since I looked into it, but I do recall a court case that ruled delivering an invoice by email was considered the same as using the USPS.
The software just increments a counter when the invoice is opened and calls the url for the image. The image url is only used in the customer's email and it has a unique id. The url points to a server side perl script that associates the id with an invoice and increments a counter if some tests are successful.
So, while I'm sure one could probably figure out how to spoof the counter the process is obscure enough to make that improbable.
The software just increments a counter when the invoice is opened and calls the url for the image. The image url is only used in the customer's email and it has a unique id. The url points to a server side perl script that associates the id with an invoice and increments a counter if some tests are successful.
So, while I'm sure one could probably figure out how to spoof the counter the process is obscure enough to make that improbable.