I downloaded Image Target sample project and installed to my android device using Eclipse. I did changes as told in https://developer.vuforia.com/resources/dev-guide/textured-plane-target and nothing happened as i hoped. Later, i deleted .jni file from Image Target project and cleaned , built and run in my android device again, i saw the teapot on stones image. I am sure, i integrated ndk-builder carefully.
So i wonder, What actually .jni file does?