In this work we document the necessary image processing steps to recognize fiducial markers for augmented reality applications. Although we use ARToolKitPlus, we believe that it is not well, neither documented all details about how this library works. We create a new simplified library for the iPad and now it is public available. Besides, we set out some criteria for the development of augmented reality systems on iPad, a restricted device in both computing power and memory storing. iPad is a tablet with a very intuitive use and has the advantage of incorporating a display screen -with the proper size for augmented reality applications-, a camera and the necessary sensors to interact by touching the screen, a gyroscope and an accelerometer. We present three applications created with this library: (1) a booklet of species for children, where the model of the species appears virtually on a marker; (2) Japanese language learning application through cards, where the meaning of the symbols is shown using virtual models on a marker; and (3) a virtual ball on a maze, which additionally uses iPad's gyroscope and accelerometer.