How do those programs that claim to let you print from iOS devices (without an AirPrint printer) actually work?
The general solution to printing from an iPad, iPhone or iPad Touch (without having to buy an AirPrint-compatible printer) varies. Most companies selling the software usually direct the iOS device to printers on the same Wi-Fi network, or “borrow” the computer’s connection to a printer to get the job done.
Software like Printopia for Mac and FingerPrint for Windows and Mac OS X is made for the computer. These programs use the Bonjour technology — used for connecting devices together on the same local network — to let the iOS device see printers attached to the computer. The computer often needs to be turned on to allow printing, unless the printer is connected to a router or has its own built-in networking functions.
Other companies like EuroSmartz use a combination of iOS/Android apps and printer-sharing software installed on the computer. Depending on the printer you have, its manufacturer may even offer its own app for iOS printing, so check the company’s Web site.
Apple’s AirPrint technology originally worked with about a dozen HP printers, but the list of manufacturers and compatible models has grown considerably. You can see what works with AirPrint here.