title: /usr/bin/ld: cannot find -lopencv
body: <p>I tried to follow this <a href="https://www.youtube.com/watch?v=MqQB5KKJCh0" rel="nofollow">tutorial</a> to install opencv ubuntu 14.04. I created a C ++ project in QT, after the execution of this. an error message is displayed:</p>
  
  <pre><code>    g++ -m64 -o test main.o mainwindow.o moc_mainwindow.o  
       -L/usr/X11R6/lib64 -L/usr/local/lib -lopencv_core -lopencv_imgproc -lopencv_highgui -lopencv_ml -lopencv_video -lopencv_features2d -lopencv_calib3d -lopencv_objdetect -lopencv_contrib 
      -lopencv_legacy -lopencv_flann 
      -lopencv_xfeatures2d -lopencv_imgcodecs -lQt5Widgets -L/usr/lib/x86_64-linux-gnu -lQt5Gui -lQt5Core -lGL -lpthread 
  
  
  //error is here
      /usr/bin/ld: cannot find -lopencv_contrib
      /usr/bin/ld: cannot find -lopencv_legacy
      /usr/bin/ld: cannot find -lopencv_xfeatures2d
      collect2: error: ld returned 1 exit status
      make: *** [test] Error 1
      06:00:12: The process "/usr/bin/make" exited with code 2.
      Error while building/deploying project test (kit: Desktop)
      When executing step 'Make'
  </code></pre>
  
  <p>Thank you :)</p>