int main()
{
    gdImagePtr src, dst;
    int size;

    src = gdImageCreateTrueColor(1, 10);
    gdTestAssert(src != NULL);

    src->sx = 0; /* this hack forces gdImageJpegPtr() to fail */

    dst = gdImageJpegPtr(src, &size, 0);
    gdTestAssert(dst == NULL);

    gdImageDestroy(src);

    return gdNumFailures();
}
The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations.