How do I setup printer for iPad/iPhone?

I would like to use my MacBook Pro (OS X Mountain Lion), to AirPrint from our iPad and iPhones (iOS 6).

The Printer is linked up to the Canon MP240 (scanner & printer) by the USB cable and the Mac has Wifi - so I thought that it would work, but iOS devices come up with "No AirPrint Printers Found" - so does the printer need to be an AirPrint printer?

Thank you.

ATB Daniel