Hi,
I'll describe my problem with linking OpenCV 2.4.2 in Qt. I have build source OpenCV with two compilers MVSC 10 and MinGW and tried to link libraries with Qt.

1) First of all, I've tried to link libraries builded with MinGW (and cmake). But I found out, that there's no "*.lib" files only "*.dll.a". So in *.pro I've tried to link those "dll.a" files, but it don't work...
Qt Code: 
  1. INCLUDEPATH += C:/Programs/OpenCV-2.4.2/mybuildmingw/install/include
  2. INCLUDEPATH += C:/Programs/OpenCV-2.4.2/mybuildmingw/install/include/opencv
  3.  
  4. LIBS += -LC:/Programs/OpenCV-2.4.2/mybuildmingw/install/lib \
  5.         -llibopencv_highgui242
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It shows "exited with code -1073741511", so it's definitely a dll linking problem. I've tried to write "-llibopencv_highgui242.a" and "-llibopencv_highgui242.dll" and "-llibopencv_highgui242.dll.a" but nothing is working...

2) Next, I tried to link libraries builded with MVSC 10. Here are "*.lib" files so it was good with code:
Qt Code: 
  1. INCLUDEPATH += C:/Programs/OpenCV-2.4.2/mybuildmingw/install/include
  2. INCLUDEPATH += C:/Programs/OpenCV-2.4.2/mybuildmingw/install/include/opencv
  3.  
  4. LIBS += -LC:/Programs/OpenCV-2.4.2/mybuild/lib/Debug \
  5.         -lopencv_highgui242d
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And program is working with code:
Qt Code: 
  1. IplImage* img = cvLoadImage( "C:\\opencv.png" );
  2.     cvNamedWindow( "Example1", CV_WINDOW_AUTOSIZE );
  3.     cvShowImage("Example1", img);
  4.     cvWaitKey(0);
  5.     cvReleaseImage(&img);
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But if I only want to use something connected with VideoCapture or Mat for example "cv::Mat I;" if gives me the compiling error:
Qt Code: 
  1. c:\Programs\OpenCV-2.4.2\mybuildmingw\install\include\opencv2\core\mat.hpp:278: błąd:undefined reference to `cv::fastFree(void*)'
  2. c:\Programs\OpenCV-2.4.2\mybuildmingw\install\include\opencv2\core\mat.hpp:367: błąd:undefined reference to `cv::Mat::deallocate()'
  3. :-1: błąd:collect2: ld returned 1 exit status
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Do you have any ideas how to solve this problem? I would really apreciate it, because I'm fighting with it whole week...