title: Build AliceVision with dependency to OpenCV
body: <p>I'm trying to build <a href="https://github.com/alicevision/AliceVision" rel="nofollow noreferrer">AliceVision</a> via CMake for Visual Studio. Now when I set the variable <code>ALICEVISION_USE_OPENCV</code> I get the following error message when configuring via cmake-gui:</p>
  
  <pre><code>CMake Warning at C:/vcpkg/scripts/buildsystems/vcpkg.cmake:263 (_find_package):
    Found package configuration file:
  
      C:/vcpkg/installed/x64-windows/share/opencv/OpenCVConfig.cmake
  
    but it set OpenCV_FOUND to FALSE so package "OpenCV" is considered to be
    NOT FOUND.
  Call Stack (most recent call first):
    src/CMakeLists.txt:499 (find_package)
  
  
  CMake Error at src/CMakeLists.txt:515 (message):
    Failed to find OpenCV.
  </code></pre>
  
  <p>I have OpenCV installed through vcpkg. I cannot figure out what the problem is or how to solve it. I've tried to set the flag to <code>1</code> at some places manually but it doesn't help.</p>