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copied!<p>First, there is a problem with the <code>findmatch</code> loop. You shouldn't just use the haystack image as an array, because you need to subtract needle's width and height from right and bottom respectively:</p> <pre><code>public Point? findmatch(int[] haystack, int[] needle) { var firstpixel = needle[0]; for (int y = 0; y < haystack_height - needle_height; y++) for (int x = 0; x < haystack_width - needle_width; x++) { if (haystack[y * haystack_width + x] == firstpixel) { var matched = checkmatch(haystack, needle, x, y); if (matched) return (new Point(x, y)); } } return null; } </code></pre> <p>That should probably solve the problem. Also, keep in mind that there might be <strong>multiple matches</strong>. For example, if "needle" is a completely white rectangle portion of a window, there will most likely be many matches in the entire screen. If this is a possibility, modify your <code>findmatch</code> method to continue searching for results after the first one is found:</p> <pre><code>public IEnumerable<Point> FindMatches(int[] haystack, int[] needle) { var firstpixel = needle[0]; for (int y = 0; y < haystack_height - needle_height; y++) for (int x = 0; x < haystack_width - needle_width; x++) { if (haystack[y * haystack_width + x] == firstpixel) { if (checkmatch(haystack, needle, x, y)) yield return (new Point(x, y)); } } } </code></pre> <p>Next, you need to keep a habit of manually disposing all objects which implement <code>IDisposable</code>, which you have created yourself. <code>Bitmap</code> and <code>Graphics</code> are such objects, meaning that your <code>screenshot</code> method needs to be modified to wrap those objects in <code>using</code> statements:</p> <pre><code>private int[] screenshot(int x, int y, int width, int height) { // dispose 'bmp' after use using (var bmp = new Bitmap(width, height, PixelFormat.Format32bppArgb)) { // dispose 'g' after use using (var g = Graphics.FromImage(bmp)) { g.CopyFromScreen(x, y, 0, 0, bmp.Size); var bmd = bmp.LockBits( new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadOnly, bmp.PixelFormat); var ptr = bmd.Scan0; // as David pointed out, "bytes" might be // a bit misleading name for a length of // a 32-bit int array (so I've changed it to "len") var len = bmd.Stride * bmp.Height / 4; var result = new int[len]; Marshal.Copy(ptr, result, 0, len); bmp.UnlockBits(bmd); return result; } } } </code></pre> <p>The rest of the code seems ok, with the remark that it won't be very efficient for certain inputs. For example, you might have a large solid color as your desktop's background, which might result in many <code>checkmatch</code> calls. </p> <p>If performance is of interest to you, you might want to check different ways to speed up the search (something like a modified <a href="http://en.wikipedia.org/wiki/Rabin-Karp_string_search_algorithm" rel="nofollow">Rabin-Karp</a> comes to mind, but I am sure there are some existing algorithms which ensure that invalid candidates are skipped immediately).</p>

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