Why my OpenCV ROI does not change?

Question

I try to loop on an image to create several ROIs (their number can be changed) but it appears that the system can only chose one. I need that because I will try to make a LBP face detector.

Here is my loop and the displaying (it's the forst time I post something here so I hope I didn't do any mistake):

    for (i=0;i<regionPerLine*regionPerLine;i++) {
        if(i%4==0 && i!=0) {
            indexLines=0;
            indexColumns=indexColumns+height/regionPerLine;
        }
        if (i%3==0)
            color=cvScalar(c,0,0,0);
        else if (i%2==0)
            color=cvScalar(0,c,0,0);
        else 
            color=cvScalar(0,0,c,0);
        roi.x=indexLines;
        roi.y=indexColumns;
        printf("\n\n%d\t%d", roi.x, roi.y);     
        cvSetImageROI(img_copy, roi);
        cvRectangle(img_copy, cvPoint(roi.x,roi.y), cvPoint(roi.x+roi.width, roi.y+roi.height), color, CV_FILLED);
        cvResetImageROI(img_copy);
        indexLines=indexLines+width/regionPerLine;
    }
    cvShowImage("img", img);
    cvShowImage("img_copy", img_copy);

    cvWaitKey(0);

    cvDestroyWindow("img");
    cvDestroyWindow("img_copy");
    cvReleaseImage(&img);
    cvReleaseImage(&img_copy);

    return 0;
}

I change the color to see the way my ROIs are changing but when I try to display them (and obtain several color rectanges), I obtain only one blue at the top left of my image which means I think that the first one is chosen but not the others. However, when I display my index in the printf function, all the needed index are well increased as I would like to.

If someone knows what happens please let me know.

Thanks