In Instax prints, like Polaroids before them, the ink is in the frame of the print and is released as the print is forces out of the camera. This is why the image fades into view. Word to the wise though, there will never be a song "shake it like an Instax picture" because shaking an Instax image does nothing. 



Canon, Kodak and HP have all released Zink based cameras and printers with a form factor roughly similar to the new Fujifilm LiPlay. The big difference is of course the end result. The LiPlay uses Instax prints, a technology similar to Polaroids with puffy white edges and an image that develops while you watch. Zink on the other hand can produce borderless prints, but takes a bit longer to spit them out.