public static List<Point> Find(Bitmap bigBmp, Bitmap smallbmp, int tolerance)
        {
            List<Point> res = new List<Point>();
            BitmapData smallData = smallbmp.LockBits(new Rectangle(0, 0, smallbmp.Width, smallbmp.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
            BitmapData bigData = bigBmp.LockBits(new Rectangle(0, 0, bigBmp.Width, bigBmp.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);

            int smallStride = smallData.Stride;
            int bigStride = bigData.Stride;

            int bigWidth = bigBmp.Width;
            int bigHeight = bigBmp.Height - smallbmp.Height + 1;
            int smallWidth = smallbmp.Width * 3;
            int smallHeight = smallbmp.Height;

            Point location = new Point();
            int margin = tolerance;
            unsafe
            {
                byte* pSmall = (byte*)(void*)smallData.Scan0;
                byte* pBig = (byte*)(void*)bigData.Scan0;

                int smallOffset = smallStride - smallbmp.Width * 3;
                int bigOffset = bigStride - bigBmp.Width * 3;

                bool matchFound = true;

                for (int y = 0; y < bigHeight; y++)
                {
                    for (int x = 0; x < bigWidth; x++)
                    {
                        byte* pBigBackup = pBig;
                        byte* pSmallBackup = pSmall;

                        //Look for the small picture.
                        for (int i = 0; i < smallHeight; i++)
                        {
                            int j = 0;
                            matchFound = true;
                            for (j = 0; j < smallWidth; j++)
                            {
                                //With tolerance: pSmall value should be between margins.
                                int inf = pBig[0] - margin;
                                int sup = pBig[0] + margin;
                                if (sup < pSmall[0] || inf > pSmall[0])
                                {
                                    matchFound = false;
                                    break;
                                }

                                pBig++;
                                pSmall++;
                            }

                            if (!matchFound) break;

                            //We restore the pointers.
                            pSmall = pSmallBackup;
                            pBig = pBigBackup;

                            //Next rows of the small and big pictures.
                            pSmall += smallStride * (1 + i);
                            pBig += bigStride * (1 + i);
                        }

                        //If match found, we return.
                        if (matchFound)
                        {
                            location.X = x;
                            location.Y = y;
                            res.Add(location);
                        }
                        //If no match found, we restore the pointers and continue.
                        pBig = pBigBackup;
                        pSmall = pSmallBackup;
                        pBig += 3;
                    }
                    if (matchFound) break;
                    pBig += bigOffset;
                }
            bigBmp.UnlockBits(bigData);
            smallbmp.UnlockBits(smallData);
            return res;
            }
        }