using System;
using System.Diagnostics;
using System.Drawing;
 
namespace ConsoleApplication1
{
    class Program
    {
        private struct RECT
        {
            public int Left;
            public int Top;
            public int Right;
            public int Bottom;
        }
 
        [System.Runtime.InteropServices.DllImport("User32.dll")]
        private static extern bool PrintWindow(IntPtr hwnd, IntPtr hDC, uint nFlags);
        [System.Runtime.InteropServices.DllImport("User32.dll")]
        private static extern bool GetClientRect(IntPtr hWnd, out RECT lpRect);
 
        static void Main(string[] args)
        {
            //ハンドルの取得
            var targetProccess = Process.GetProcessesByName("devenv")[0];//ここでは最初の一つを対象にした
            var handle = targetProccess.MainWindowHandle;
            //保存対象の画像処理
            var rec = new RECT();
            var size = GetClientRect(handle, out rec);
            var img = new Bitmap(rec.Right - rec.Left, rec.Bottom);
            var memg = Graphics.FromImage(img);
            IntPtr dc = memg.GetHdc();
            PrintWindow(handle, dc, 0);
            memg.ReleaseHdc(dc);
            memg.Dispose();
            //画像保存
            img.Save("画像.png");
        }
    }
}