ProxyTrans transform filter would call your function as a callback
on every frame instead of processing the image itself. If you
create a filter graph with your application, insert the proxy
filter before renderer (or at any other place you like) and set a
callback function defined in the application; the proxy implements
the special interface for such case -- IProxyTrans. Then start the
DS and every frame will be processed with your function. You can
find the binary of ProxyTrans in Bin folder of your OpenCV
installation. Here is the example of using ProxyTrans. Also refer
to Apps\Hawk\MainFrm.cpp and Apps\Hawk\AviSource.cpp.

#include <iProxyTrans.h>
#include <ProxyTransuids.h>

void callback(void*);

int Initialize()
{
/* Initialize the source filter, filter graph.
Find the samples of those in Apps\Hawk\MainFrm.cpp, functions
CMainFrame::CreateCamera and CMainFrame::CreateFilterGraph */

    IProxyTransform* pProxyTrans = NULL;
    // Create a proxy transform filter
    if(FAILED(CoCreateInstance(CLSID_ProxyTransform, NULL,
CLSCTX_INPROC_SERVER,
                IID_IProxyTransform, (void**)&pProxyTrans))
|| !pProxyTrans)
    {
        return -1;
    }
    IBaseFilter* pProxyFilter = NULL;
    pProxyTrans->QueryInterface(IID_IBaseFilter, (void**)&pProxyFilter);

    // Set the proxy callback
    pProxyTrans->set_transform((void(*)(void*))callback, 0);

    /* Connect the filters together and run DS, see the samples mentioned above */
}

void callback(void* _image)
{
    IplImage* image = (IplImage*)_image;
    /* process the frame as usual IplImage.
    No image data is copied by ProxyTrans, it just creates an
    IplImage structure that points to the data. Right now the data
    format is restricted to 24 bits bmp which is a common case. */
}