OpenCV static linking error - opencv

Question

I want to use OpenCV as a static library. After compiling the library as a static library now i'm testing with some examples to see all the dependencies.
The dependencies added to compile are -staticpkg-config --libs opencv-lpthread -ljpeg -ltiff -lz -ljasper -lpng12
But obtain the following Error message:
g++ -c -g -Wall -O2 `pkg-config --cflags opencv` formas.cpp
g++ -g -Wall -O2 `pkg-config --cflags opencv` formas.o -o paint -static `pkg-config --libs opencv` -lpthread -ljpeg -ltiff -lz -ljasper -lpng12
/usr/local/lib/libopencv_core.a(system.o): In function `cv::tempfile(char const*)':
system.cpp:(.text._ZN2cv8tempfileEPKc+0x3a): warning: the use of `tmpnam' is dangerous, better use `mkstemp'
/usr/local/lib/libopencv_core.a(system.o): In function `cv::getTickCount()':
system.cpp:(.text._ZN2cv12getTickCountEv+0x2a): undefined reference to `clock_gettime'
/usr/local/lib/libopencv_highgui.a(grfmt_png.o): In function `cv::PngDecoder::readHeader()':
grfmt_png.cpp:(.text._ZN2cv10PngDecoder10readHeaderEv+0xde): undefined reference to `png_set_longjmp_fn'
/usr/local/lib/libopencv_highgui.a(grfmt_png.o): In function `cv::PngEncoder::write(cv::Mat const&, std::vector<int, std::allocator<int> > const&)':
grfmt_png.cpp:(.text._ZN2cv10PngEncoder5writeERKNS_3MatERKSt6vectorIiSaIiEE+0x134): undefined reference to `png_set_longjmp_fn'
/usr/local/lib/libopencv_highgui.a(grfmt_png.o): In function `cv::PngDecoder::readData(cv::Mat&)':
grfmt_png.cpp:(.text._ZN2cv10PngDecoder8readDataERNS_3MatE+0x141): undefined reference to `png_set_longjmp_fn'
collect2: ld returned 1 exit status
make: *** [all] Error 1
I made something wrong or there an error in OpenCV library.
OpenCV version: 2.3.1 (latest version)
formas --> example which create an image an draw some figures and save into a file. So simple.
Thanks in advance.

Answer 1

It seems you have compiled OpenCV with libpng 1.4 or newer but trying to link with libpng 1.2
What cmake command have you used to configure OpenCV?
Update:
You need to add -lrt to the list of libraries you link for the clock_gettime function.