Add the following code,

const char* opencv_libraries = 0;
const char* addon_modules = 0;
cvGetModuleInfo( 0, &opencv_libraries, &addon_modules );
printf( “OpenCV: %s\nAdd-on Modules: %s\n”, opencv_libraries, addon_modules );

When IPP is detected, it will print something like this:
OpenCV: cxcore: beta 4.1 (0.9.7), cv: beta 4.1 (0.9.7)
Add-on modules: ippcv20.dll, ippi20.dll, ipps20.dll, ippvm20.dll

Then the IPP version of the function will be loaded automatically.
http://www.intel.com/support/performancetools/libraries/ipp/sb/cs-010656.htm
Learning-Based Computer Vision with Intel’s Open Source Computer Vision Library
http://www.intel.com/technology/itj/2005/volume09issue02/art03_learning_vision/p01_abstract.htm

How to turn off IPP? And turn on it again?
cvUseOptimized(0); …cvUseOptimized(1);

用了这么多年opencv和ipp了，还不清楚opencv原来可以自动调用ipp的函数。。。