1) Direct Answer:
Try this:
sudo updatedb
locate OpenCVConfig.cmake
For me, I get:
/home/pkarasev3/source/opencv/build/OpenCVConfig.cmake
To see the version, you can try:
cat /home/pkarasev3/source/opencv/build/OpenCVConfig.cmake
giving
....
SET(OpenCV_VERSION 2.3.1)
....
2) Better Answer:
"sudo make install" is your enemy, don't do that when you need to compile/update the library often and possibly debug step through it's internal functions. Notice how my config file is in a local build directory, not in /usr/something. You will avoid this confusion in the future, and can maintain several different versions even (debug and release, for example).
Edit: the reason this questions seems to arise often for OpenCV as opposed to other libraries is that it changes rather dramatically and fast between versions, and many of the operations are not so well-defined / well-constrained so you can't just rely on it to be a black-box like you do for something like libpng or libjpeg. Thus, better to not install it at all really, but just compile and link to the build folder.
