A bit of refactoring to be able to find some issue...

GreenshotPlugin/UnmanagedHelpers/SafeWindowDcHandle.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Runtime.InteropServices;
+using System.Security;
+using System.Security.Permissions;
+using Microsoft.Win32.SafeHandles;
+
+namespace GreenshotPlugin.UnmanagedHelpers
+{
+    /// <summary>
+    /// A WindowDC SafeHandle implementation
+    /// </summary>
+    public class SafeWindowDcHandle : SafeHandleZeroOrMinusOneIsInvalid {
+        [DllImport("user32", SetLastError = true)]
+        private static extern IntPtr GetWindowDC(IntPtr hWnd);
+        [DllImport("user32", SetLastError = true)]
+        private static extern bool ReleaseDC(IntPtr hWnd, IntPtr hDC);
+
+        private readonly IntPtr _hWnd;
+
+        /// <summary>
+        /// Needed for marshalling return values
+        /// </summary>
+        public SafeWindowDcHandle() : base(true)
+        {
+        }
+
+        [SecurityCritical]
+        public SafeWindowDcHandle(IntPtr hWnd, IntPtr preexistingHandle) : base(true) {
+            _hWnd = hWnd;
+            SetHandle(preexistingHandle);
+        }
+
+        [SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode=true)]
+        protected override bool ReleaseHandle() {
+            bool returnValue = ReleaseDC(_hWnd, handle);
+            return returnValue;
+        }
+
+        /// <summary>
+        /// Creates a DC as SafeWindowDcHandle for the whole of the specified hWnd
+        /// </summary>
+        /// <param name="hWnd">IntPtr</param>
+        /// <returns>SafeWindowDcHandle</returns>
+        public static SafeWindowDcHandle FromWindow(IntPtr hWnd)
+        {
+            if (hWnd == IntPtr.Zero)
+            {
+                return null;
+            }
+            var hDcDesktop = GetWindowDC(hWnd);
+            return new SafeWindowDcHandle(hWnd, hDcDesktop);
+        }
+
+        public static SafeWindowDcHandle FromDesktop() {
+            IntPtr hWndDesktop = User32.GetDesktopWindow();
+            IntPtr hDCDesktop = GetWindowDC(hWndDesktop);
+            return new SafeWindowDcHandle(hWndDesktop, hDCDesktop);
+        }
+    }
+}