This contains a fix for SUPPORT-288 which was suggested by Raymond Chen here: https://devblogs.microsoft.com/oldnewthing/20200302-00/?p=103507

GreenshotPlugin/UnmanagedHelpers/DWM.cs

@@ -0,0 +1,117 @@
+/*
+ * Greenshot - a free and open source screenshot tool
+ * Copyright (C) 2007-2020 Thomas Braun, Jens Klingen, Robin Krom
+ * 
+ * For more information see: http://getgreenshot.org/
+ * The Greenshot project is hosted on GitHub https://github.com/greenshot/greenshot
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 1 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+using System;
+using System.Drawing;
+using System.Runtime.InteropServices;
+using GreenshotPlugin.Core;
+using GreenshotPlugin.UnmanagedHelpers.Enums;
+using GreenshotPlugin.UnmanagedHelpers.Structs;
+using Microsoft.Win32;
+
+namespace GreenshotPlugin.UnmanagedHelpers {
+
+    /// <summary>
+	/// Description of DWM.
+	/// </summary>
+	public static class DWM {
+		public static readonly uint DWM_EC_DISABLECOMPOSITION = 0;
+		public static readonly uint DWM_EC_ENABLECOMPOSITION = 1;
+
+		// DWM
+		[DllImport("dwmapi", SetLastError = true)]
+		public static extern int DwmRegisterThumbnail(IntPtr dest, IntPtr src, out IntPtr thumb);
+		[DllImport("dwmapi", SetLastError = true)]
+		public static extern int DwmUnregisterThumbnail(IntPtr thumb);
+		[DllImport("dwmapi", SetLastError = true)]
+		public static extern int DwmQueryThumbnailSourceSize(IntPtr thumb, out SIZE size);
+		[DllImport("dwmapi", SetLastError = true)]
+		public static extern int DwmUpdateThumbnailProperties(IntPtr hThumb, ref DWM_THUMBNAIL_PROPERTIES props);
+
+		// Deprecated as of Windows 8 Release Preview
+		[DllImport("dwmapi", SetLastError = true)]
+		public static extern int DwmIsCompositionEnabled(out bool enabled);
+		[DllImport("dwmapi", SetLastError = true)]
+		public static extern int DwmGetWindowAttribute(IntPtr hWnd, DWMWINDOWATTRIBUTE dwAttribute, out RECT lpRect, int size);
+        [DllImport("dwmapi", SetLastError = true)]
+        public static extern int DwmGetWindowAttribute(IntPtr hWnd, DWMWINDOWATTRIBUTE dwAttribute, out bool pvAttribute, int cbAttribute);
+		[DllImport("dwmapi", SetLastError = true)] 
+		public static extern int DwmEnableBlurBehindWindow(IntPtr hWnd, ref DWM_BLURBEHIND blurBehind);
+		[DllImport("dwmapi", SetLastError = true)]
+		public static extern uint DwmEnableComposition(uint uCompositionAction);
+
+		public static void EnableComposition() {
+			DwmEnableComposition(DWM_EC_ENABLECOMPOSITION);
+		}
+		public static void DisableComposition() {
+			DwmEnableComposition(DWM_EC_DISABLECOMPOSITION);
+		}
+
+		// Key to ColorizationColor for DWM
+		private const string COLORIZATION_COLOR_KEY = @"SOFTWARE\Microsoft\Windows\DWM";
+
+		/// <summary>
+		/// Checks if the window is cloaked, this should solve some issues with the window selection code
+		/// </summary>
+		/// <param name="hWnd">IntPtr as hWmd</param>
+		/// <returns>bool</returns>
+		public static bool IsWindowCloaked(IntPtr hWnd)
+        {
+			if (WindowsVersion.IsWindows8OrLater)
+            {
+                return false;
+            }
+
+            DwmGetWindowAttribute(hWnd, DWMWINDOWATTRIBUTE.DWMWA_CLOAKED, out bool isCloaked, sizeof(bool));
+			return isCloaked;
+        }
+
+        /// <summary>
+		/// Helper method for an easy DWM check
+		/// </summary>
+		/// <returns>bool true if DWM is available AND active</returns>
+		public static bool IsDwmEnabled() {
+			// According to: http://technet.microsoft.com/en-us/subscriptions/aa969538%28v=vs.85%29.aspx
+			// And: http://msdn.microsoft.com/en-us/library/windows/desktop/aa969510%28v=vs.85%29.aspx
+			// DMW is always enabled on Windows 8! So return true and save a check! ;-)
+			if (WindowsVersion.IsWindows8OrLater) {
+				return true;
+			}
+			if (WindowsVersion.IsWindowsVistaOrLater) {
+                DwmIsCompositionEnabled(out var dwmEnabled);
+				return dwmEnabled;
+			}
+			return false;
+		}
+
+		public static Color ColorizationColor {
+			get {
+				using (RegistryKey key = Registry.CurrentUser.OpenSubKey(COLORIZATION_COLOR_KEY, false)) {
+					object dwordValue = key?.GetValue("ColorizationColor");
+					if (dwordValue != null) {
+						return Color.FromArgb((int)dwordValue);
+					}
+				}
+				return Color.White;
+			}
+		}
+	}
+}