I have been building an complete Invoice / Cashier system for Cafés in my spare time for quite some time. It consists of an server, running the web app, an laptop to use as the real cashier system, multiple Android Phones as a way for the waiters to enter their orders and two Raspberry Pis with Brother QL-570s as Invoice Printers. One of those is set at the counter, printing the "normal invoice", the second one is located at the kitchen and got some special routing logic, so that it only recieves the items actually produced in the kitchen. However, as I was using these special kind of printers, I was bound to use the printer-ptouch drivers... and yeah, they are *kind of* buggy. Buggy in that way, that, after installing them with cups and hacking your paper media in there - they will just stop working from time to time. Without further warning. They will stop printing just somewhere in the middle of the job. I really tried all options available to me now - and was now keen on finding *other* kinds of solutions. And after two days of searching, I stumpled upon this master piece: https://github.com/pklaus/brother_ql. Mr. Philipp Klaus did actually dump the whole cups and printer server stuff and directly converted png files into the needed binary code for the printer. And not only the QL-570, but other types as well. I really recommend checking out his code and trying his way on printing - its a huge timesaver, especially on embedded devices like the Raspberry Pi :)!