how could we install opencv on anaconda?

I guess

http://answers.opencv.org/question/17536/install-opencv-for-anaconda-ipython/

it would be an answer

If you compile OpenCV from source, and Anaconda is your default python interpretor 
(CMake rule PYTHON_PACKAGES_PATH = C:\Anaconda\Lib\site-packages), 
then the install rule will copy cv2.pyd to C:\Anaconda\Lib\site-packages.
Otherwise, you could do it manually, and make sure OpenCV libs are in the PATH.

Still I don't know what is CMake rule(?) and "install rule".

Run the following command:

conda install -c https://conda.binstar.org/menpo opencv

I realized that opencv3 is also available now, run the following command:

conda install -c https://conda.binstar.org/menpo opencv3

Edit on Aug 18, 2016: You may like to add the "menpo" channel permanently by:

conda config --add channels menpo

And then opencv can be installed by:

conda install opencv(or opencv3)

Edit on Aug 14, 2017: "clinicalgraphics" channel provides relatively newer vtk version for very recent python3

conda install -c clinicalgraphics vtk