augmented reality framework

There are two types of augmented reality:

a) marker based, which needs bidimensional markers to recognize using computer vision and image analysis to draw an image over them with the corresponding rotation (ARToolkit)

b) geolocation and orientation based, which means that the app knows the exact position in the earth where you are, and what are you facing and it computes what you see, based on geolocation. (layar,wikitude)

Apps like junaio mixes both of them

You can also use the new Qualcomm AR SDK http://developer.qualcomm.com/dev/augmented-reality

For ideas, you could look at the following:

Existing Apps and their APIs: There are number of Augmented Reality applications in the Android market of which Layar and Wikitude are well known. Others like SomaView and GeoVector also exist. AFAIK, Wikitude and Layar have made their API's public.

Toolkit: There is also a toolkit named, NyARToolkit that provides a library for such a thing.

Tutorial: DevX Article by Chris Haseman

Good Luck!