How to remember a previous image with OpenCV in a loop?

I have about 300 images which I want to process in a loop. In every iteration I want to compare an image with an image from the previous loop.

I am trying to hold the current image in:

fIplImageHeader 

The image from the previous iteration is stored in:

lastF开发者_如何学PythonIplImageHeader 

This is how I am doing it and it is giving me an exception:

for ( int i = 0; i < 300; i++ )
{
        // get the path to an image (images are named 0.jpg, 1.jpg etc)
        // filePath.c_str() contains the path to an image

        // load the current image to an IplImage object
        IplImage* fIplImageHeader = cvLoadImage( filePath.c_str() );

        // create a header for te previous image
        IplImage* lastFIplImageHeader = cvCreateImageHeader( 
            cvSize( fIplImageHeader->width, fIplImageHeader->height ),
            fIplImageHeader->depth, fIplImageHeader->nChannels 
        );

        if ( NULL != lastFIplImageHeader->imageData )
        {
            // COMPARE IMAGES HERE
            // only if we are already in 2nd + iteration
        }

        // copy the current image to the lastFIplImageHeader
        // which will hold it in the next iteration
        if ( lastFIplImageHeader )
        {
            cvReleaseImage( &lastFIplImageHeader );
        }
        cvCopy(fIplImageHeader , lastFIplImageHeader);

        // do stuff

        if ( fIplImageHeader )
        {
            cvReleaseImage( &fIplImageHeader );
        }

}

The exception:

First-chance exception at 0x753cb727 in Client.exe: Microsoft C++ exception: cv::Exception at memory location 0x0036ef5c.. 
Unhandled exception at 0x753cb727 in Client.exe: Microsoft C++ exception: cv::Exception at memory location 0x0036ef5c..

I suggest you load the first image outside the loop and iterate from i=1. You did not show how (if at all) you initialized lastFIplImageHeader and fIplImageHeader outside the loop.
In the line if ( NULL != lastFIplImageHeader->imageData ) there is no test that lastFIplImageHeader itself is not null.
I suggest you add a whole bunch of assert()s to verify that the data you use is actually valid when you try to operate on it.