camera calibration: corner count:0 - camera

Question

we are trying to implement camera calibration but the corner count output is zero.Here is the code attached.In this we are giving static images with height and width 12.
cvFindChessboardCorners this function is not working as expected. Can someone please help with this error
#include "opencv\cv.h"
#include "opencv\highgui.h"
#include "conio.h"
#include "stdio.h"
#include "string.h"
#define N 10
int n_boards = 0; //Number of snapshots of the chessboard
int board_w; //Enclosed corners horizontally on the chessboard
int board_h; //Enclosed corners vertically on the chessboard
int main()
{
int start, total;
char str[15],ext[15];
int board_h = 0, board_w = 0;
printf("Enter the name of the Images (String) without numeric denominator: ");
scanf( "%s", str);
printf("Enter the extension of the Images (String): ");
scanf( "%s", ext);
printf("Enter the total number of the File (should be integer) starting with index << 1 >> :: ");
scanf( "%d", &total);
printf("Enter the the board width (should be integer) :: ");
scanf( "%d", &board_w);
printf("Enter the the board height (should be integer) :: ");
scanf( "%d", &board_h);
n_boards = total;
//board_w = 12;
//board_h = 12;
int board_total = board_w * board_h; //Total enclosed corners on the board
CvSize board_sz = cvSize( board_w, board_h );
//Allocate storage for the parameters according to total number of corners and number of snapshots
CvMat* image_points = cvCreateMat(n_boards*board_total,2,CV_32FC1);
CvMat* object_points = cvCreateMat(n_boards*board_total,3,CV_32FC1);
CvMat* point_counts = cvCreateMat(n_boards,1,CV_32SC1);
CvMat* intrinsic_matrix = cvCreateMat(3,3,CV_32FC1);
CvMat* distortion_coeffs = cvCreateMat(4,1,CV_32FC1);
CvPoint2D32f* corners = new CvPoint2D32f[ board_total ];
int corner_count;
int successes = 0;
int step, frame = 0;
char imgstr[N][8];
for(int i = 1; i<= total; i++)
{
sprintf(imgstr[i-1], "%s%d", str, i);
strcat(imgstr[i-1],".");
strcat(imgstr[i-1],ext);
}
printf("Loading Images....... \n\n");
IplImage* image;
IplImage *gray_image ;
cvNamedWindow( "Snapshot" );
int k = 0;
for(int i= 0; i< total;i++)
{
image = cvLoadImage(imgstr[i],1);
if(image==NULL )
{
printf("unable to load the frame --> %s\n",imgstr[i]);exit(0);
}
gray_image = cvCreateImage(cvGetSize(image),8,1);
//Find chessboard corners:
int found = cvFindChessboardCorners(image, board_sz, corners, &corner_count,CV_CALIB_CB_ADAPTIVE_THRESH | CV_CALIB_CB_FILTER_QUADS | CV_CALIB_CB_NORMALIZE_IMAGE );
printf("Corner count for %s is << %d >> \n",imgstr[i],corner_count);
}
return 0;
}