Screenshot secure desktop

Question

I am working with screen sharing project.I am capturing desktop screen using below function.it works fine. But whenever secure desktop prompting for elevation .it returns black/empty image.

But when i turn off secured desktop from local security policy.It works fine.

Is there any way to capture secure desktop without disabling Local Security Policy.

static Bitmap CaptureDesktop()
{
    SIZE size;
    Bitmap printscreen = null;

    size.cx = Win32Stuff.GetSystemMetrics
                     (Win32Stuff.SM_CXSCREEN);

    size.cy = Win32Stuff.GetSystemMetrics
              (Win32Stuff.SM_CYSCREEN);

    int width = size.cx; int height = size.cy;

    IntPtr hWnd = Win32Stuff.GetDesktopWindow();
    IntPtr hDC = Win32Stuff.GetDC(hWnd);
    if (hDC != IntPtr.Zero)
    {
        IntPtr hMemDC = GDIStuff.CreateCompatibleDC(hDC);
        if (hMemDC != IntPtr.Zero)
        {
            IntPtr m_HBitmap = GDIStuff.CreateCompatibleBitmap(hDC, width, height);
            if (m_HBitmap != IntPtr.Zero)
            {
                IntPtr hOld = (IntPtr)GDIStuff.SelectObject(hMemDC, m_HBitmap);
                GDIStuff.BitBlt(hMemDC, 0, 0, width, height, hDC, 0, 0, GDIStuff.SRCCOPY);
                GDIStuff.SelectObject(hMemDC, hOld);
                GDIStuff.DeleteDC(hMemDC);
                printscreen = System.Drawing.Image.FromHbitmap(m_HBitmap);
                GDIStuff.DeleteObject(m_HBitmap);
            }
        }
    }
    Win32Stuff.ReleaseDC(hWnd, hDC);

    return printscreen;
}

Edit :

1. Exe Installed in Secured location
2. Exe is digitally signed

Answer 1

In order to get the screen contents of the Secure Desktop, your application needs to fulfill some special criteria:

• it must run under the SYSTEM account, not the logged-on user account
• it must run on the Winlogon desktop, not on the user desktop
• it should run as a service

To test it, you could eg use the SysInternals PsExec tool to run your application in that mode:

PsExec /h /x /d /s "path_to\your_application.exe"

The /x and /s switches are important: they run the process under the SYSTEM account and on the Winlogon desktop.

If you want to avoid using third-party tools, you need to create your own Windows service which will perform the screen captures of the Secure Desktop.

There is no source code of PsExec available, but you can look at the PAExec tool's source code - it's an open source alternative.