Q:

Should I use JavaCV or OpenCV's java library on Android? 

http://opencv.willowgarage.com/wiki/Android or http://code.google.com/p/javacv/ ? 
I am new to computer vision, and want to do something on the phone camera such as matching the current screen to the most similar image in the database. 
Both of them are java, what are the differences?  Which one should I use? 
Thank you so much for helping! 

A:

JavaCV is a wrapper around some native libraries, including OpenCV.  

In any case you are going to use OpenCV, either directly by writing your own wrapper or using OpenCV's Android wrappers or using JavaCV. 
As said JavaCV uses several libs, so it has many more features than only OpenCV.  If you need those features than naturally you'd choose JavaCV.