This looks interesting if you’re interested in AR type stuff:
Many developers ask me about natural feature tracking SDKs for mobile devices. One of the cool SDKs I like is the String SDK.
If you are already familiar with AR you’ll notice that String lives somewhere in middle of fiduciary markers and natural feature tracking. Tracking images combines the high contrast black border of a marker and a complex natural image in the centre. This mix actually works well. With a marker users can identify it as having special significance when presented to a camera (much the same way users identify QR Codes as having significance). With NTF images the challenge is telling the user that the image as has significance without providing a large amount of instructions. Combining the two therefore goes someway to solve the identification problem.
The String SDK which is currently available for iOS with an Android version in the works is powerful enough to build some pretty amazing solutions…
Doesn’t seem to be available for general download yet, but the contact form is here.