I have a simple console application program that captures a screenshot
of the display device and then saves the image to file as a bitmap.
The screenshot is generated successfully when run with my
(administrative) account, but when run under the local system account
it fails. Specifically, the StretchBlt( ) function fails and last
error is set to 5 (access denied).

The sequence of Windows API calls is as follows:

          HDC sourceDC =
          CreateDC( L"DISPLAY",        // lpszDriver - driver name
                          NULL,                  // lpszDevice -
device name
                          NULL,                  // lpszOutput - not
used; should be NULL
                          NULL );

          HDC memoryDC =
          CreateCompatibleDC( sourceDC );

          HBITMAP bitmap =
          CreateCompatibleBitmap( sourceDC,                    //
hdc     - handle to DC

horizontalResolution,    // nWidth  - width of bitmap, in pixels
                                                 verticalResolution );

          SelectObject( memoryDC, // hdc     - handle to DC
                               bitmap );

          StretchBlt( memoryDC,                          //
hdcDest      - handle to destination DC

0,                                        // nXOriginDest - x-coord of
destination upper-left corner

0,                                        // nYOriginDest - y-coord of
destination upper-left corner
                           horizontalResolution,            //
nWidthDest   - width of destination rectangle
                           verticalResolution,                //
nHeightDest  - height of destination rectangle
                           sourceDC,                            //
hdcSrc       - handle to source DC

0,                                        // nXOriginSrc  - x-coord of
source upper-left corner

0,                                        // nYOriginSrc  - y-coord of
source upper-left corner
                           sourceHorizonalResolution,    //
nWidthSrc    - width of source rectangle
                           sourceVerticalResolution,      //
nHeightSrc   - height of source rectangle
                           SRCCOPY );

(Note: For clarity, I have omitted error checking code from the above
excerpt. I am evaluating and handling the return value of every
function.).

All operations up until the StretchBlt function succeed.

Anyone know of any reason why this would fail when run under the
system account? I have reproduced this on several systems including XP
Pro and Vista.

Thanks for your help.