What is OpenCV
OpenCV is an open source C++ library for image processing and computer vision application originally developed by Intel.It is free for both commercial and non-commercial usage. computer vision defers from image processing,in computer vision image and its characteristics treated as a signal. based on the signal different activity can be computed in computer programs.More than 500 different algorithms have been implemented in OpenCV and exposed as c/c++ API. Usage ranges from interactive art, to mines inspection, stitching maps ,etc.
you can download for windows,linux,android etc from
Building and installing OpenCV for Linux
$ wget http://sourceforge.net/projects/opencvlibrary/files/opencv-unix/2.4.7/opencv-2.4.7.tar.gz/download
$ tar -xzvf opencv-2.4.7.tar.gz
$ cd opencv-2.4.7
# mkdir build
# cd build
# cmake -D WITH_TBB=ON -D INSTALL_C_EXAMPLES=ON
# make install
In build directory you can run example code , the best way to learn opencv by example code.