[Snippet] Capture Window Screenshot

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Diagnostics;
using System.Threading;

        [DllImport("User32.dll")]
        public static extern Int32 SetForegroundWindow(int hWnd);

        [DllImport("user32.dll")]
        static extern bool GetWindowRect(int hwnd, out Rectangle lpRect);

        Image CaptureWindowScreenshot(string processName, int processInstanceIndex)
        {
            int processMainWindowHandle = Process.GetProcessesByName(processName)[processInstanceIndex].MainWindowHandle.ToInt32();
            SetForegroundWindow(processMainWindowHandle);
            Thread.Sleep(500);
            Rectangle rectangle = new Rectangle();
            GetWindowRect(processMainWindowHandle, out rectangle);
            Image windowScreenshot = (Image)new Bitmap(rectangle.Width, rectangle.Height);
            using (Graphics graphics = Graphics.FromImage(windowScreenshot))
            {
                //graphics.CompositingMode = CompositingMode.SourceCopy;
                //graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;
                //graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
                //graphics.CompositingQuality = CompositingQuality.HighQuality;
                //graphics.SmoothingMode = SmoothingMode.AntiAlias;
                graphics.CopyFromScreen(rectangle.Location, rectangle.Location, rectangle.Size);
            }
            return windowScreenshot;
        }

            Image windowScreenshot;
            try
            {
                windowScreenshot = CaptureWindowScreenshot("processName", 0);
                windowScreenshot.Save("windowScreenshot.png");
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }