Comparing current and previous faces from a continous faces detection - c++

Question

I am working with face detection.I need to compare current and previous(successive) faces.Can any one help me how to take current and previous faces from a continuous face detection.I am not getting any idea about this.
This is my face detection code
void facedetect(IplImage* image)
{
ct1++;
cvNamedWindow("output");
int j=0,i,count=0,strsize;
char numstr[50];
CvPoint ul,lr,w,h,ul1,lr1;
CvRect *r;
string path;
IplImage* image1;IplImage* tmpsize;IplImage* reimg;
CvHaarClassifierCascade* cascade=(CvHaarClassifierCascade*) cvLoad(cascade_name);
CvMemStorage* storage=cvCreateMemStorage(0);
const char *extract;
if(!cascade)
{
cout<<"Coulid not load classifier cascade"<<endl;
}
if(cascade)
{ faces=cvHaarDetectObjects(image,cascade,storage,1.1,1,CV_HAAR_DO_CANNY_PRUNING,cvSize(10,10));
for(int i=0;i<(faces ? faces->total : 0);i++)
{
string s1="im",re,rename,ex=".pgm";
sprintf(numstr, "%d", k);
re = s1 + numstr;
rename=re+ex;
char *extract1=new char[rename.size()+1];
extract1[rename.size()]=0; memcpy(extract1,rename.c_str(),rename.size());
strsize=rename.size();
r=(CvRect*) cvGetSeqElem(faces,i);
ul.x=r->x;
ul.y=r->y;
w.x=r->width;
h.y=r->height;
lr.x=(r->x + r->width);
lr.y=(r->y + r->height);
cvSetImageROI(image,cvRect(ul.x,ul.y,w.x,h.y));
image1=cvCreateImage(cvGetSize(image),image->depth,image->nChannels);
cvCopy(image, image1, NULL);
reimg=resizeImage(image1, 40, 40, true);
saveImage(reimg,extract1);
Mat img=cvarrToMat(reimg);
//Mat img1=cvarrToMat();
imshow("result",img); //this is the current image, but i need to get the previous image also.
//readImag(img,"/home/athira/Image/folderr", path);
cvResetImageROI(image);
cvRectangle(image,ul,lr,CV_RGB(1,255,0),3,8,0);
j++,count++;
k++;
arr[l]=ul.x;
arr1[l]=ul.y;
cout<<"frame"<<ct1<<" "<<"face"<<ct<<":"<<"x: "<<ul.x<<endl;
cout<<"frame"<<ct1<<" "<<"face"<<ct<<":"<<"y: "<<ul.y<<endl;
cout<<""<<endl;
ct++;
//compareImages(l,faces->total);
//feature_extract(img,img1);
l++;
}
width=image->width;
height=image->height;
resoltion=width*height;
s=(float) 0.0301/100;
diff=s*resoltion;
cvShowImage("output",image);
cvWaitKey(0);
}
}