公共方法：

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.ComTypes;
using System.Security;
using System.Windows.Forms;


namespace mVIM_WebSite.WebForms.Reservation
{
    /// <summary>
    ///     圖片型別列舉
    /// </summary>
    public enum ImageType
    {
        GIF = 0,
        JPG = 1,
        PNG = 2
    }


    /// <summary>
    ///     圖片輔助類
    /// </summary>
    /// 


    public class ImageHelper
    {
        /// <summary>
        ///     將Url地址儲存為圖片
        /// </summary>
        /// <param name="url">網頁路徑</param>
        /// <param name="savePath">圖片存放路徑</param>
        /// <param name="imageType">圖片型別</param>
        /// <returns></returns>
        [System.STAThread]
        public static string SaveUrlToImage(string url, string savePath, ImageType imageType)
        {
            var uri = new Uri(url);
            using (var bit = GetHtmlImage(uri, Screen.PrimaryScreen.Bounds.Width))
            {
                switch (imageType)
                {
                    case ImageType.GIF:
                        bit.Save(savePath, ImageFormat.Gif);
                        break;
                    case ImageType.JPG:
                        bit.Save(savePath, ImageFormat.Jpeg);
                        break;
                    case ImageType.PNG:
                        bit.Save(savePath, ImageFormat.Png);
                        break;
                    default:
                        bit.Save(savePath, ImageFormat.Jpeg);
                        break;
                }
                return savePath;
            }
        }


        [System.STAThread]
        protected static Bitmap GetHtmlImage(Uri urlString, int width)
        {
            using (var control = new WebBrowser { Size = new Size(width, 10), Url = urlString, ScriptErrorsSuppressed = true })
            {
                while (control.ReadyState != WebBrowserReadyState.Complete)
                {
                    Application.DoEvents();
                }
                if (control.Document != null)
                {
                    if (control.Document.Body != null)
                    {
                        control.Height = control.Document.Body.ScrollRectangle.Height + 20;
                    }
                }
                control.Url = urlString;
                var snap = new WebControlImage.Snapshot();
                var bitmap = snap.TakeSnapshot(control.ActiveXInstance, new Rectangle(0, 0, control.Width, control.Height));
                control.Dispose();
                return bitmap;
            }
        }


        /// WebBrowser獲取圖形
        protected class WebControlImage
        {
            internal static class NativeMethods
            {
                [StructLayout(LayoutKind.Sequential)]
                public sealed class TagDvtargetdevice
                {
                    [MarshalAs(UnmanagedType.U4)]
                    public int tdSize;
                    [MarshalAs(UnmanagedType.U2)]
                    public short tdDriverNameOffset;
                    [MarshalAs(UnmanagedType.U2)]
                    public short tdDeviceNameOffset;
                    [MarshalAs(UnmanagedType.U2)]
                    public short tdPortNameOffset;
                    [MarshalAs(UnmanagedType.U2)]
                    public short tdExtDevmodeOffset;
                }


                [StructLayout(LayoutKind.Sequential)]
                public class Comrect
                {
                    public int left;
                    public int top;
                    public int right;
                    public int bottom;


                    public Comrect()
                    {
                    }


                    public Comrect(Rectangle r)
                    {
                        left = r.X;
                        top = r.Y;
                        right = r.Right;
                        bottom = r.Bottom;
                    }


                    public Comrect(int left, int top, int right, int bottom)
                    {
                        this.left = left;
                        this.top = top;
                        this.right = right;
                        this.bottom = bottom;
                    }


                    public static Comrect FromXywh(int x, int y, int width, int height)
                    {
                        return new Comrect(x, y, x + width, y + height);
                    }


                    public override string ToString()
                    {
                        return string.Concat("Left = ", left, " Top ", top, " Right = ", right, " Bottom = ", bottom);
                    }
                }


                [StructLayout(LayoutKind.Sequential)]
                public sealed class TagLogpalette
                {
                    [MarshalAs(UnmanagedType.U2)]
                    public short palVersion;
                    [MarshalAs(UnmanagedType.U2)]
                    public short palNumEntries;
                }
            }


            public class Snapshot
            {
                /// 圖象大小
                public Bitmap TakeSnapshot(object pUnknown, Rectangle bmpRect)
                {
                    if (pUnknown == null)
                        return null;
                    //必須為com物件 
                    if (!Marshal.IsComObject(pUnknown))
                        return null;
                    //IViewObject 介面 
                    IntPtr viewObject;
                    //記憶體圖 
                    var bitmap = new Bitmap(bmpRect.Width, bmpRect.Height);
                    var image = Graphics.FromImage(bitmap);
                    //獲取介面 
                    object hret = Marshal.QueryInterface(Marshal.GetIUnknownForObject(pUnknown),
                        ref UnsafeNativeMethods.IidIViewObject, out viewObject);
                    try
                    {
                        var o =
                            Marshal.GetTypedObjectForIUnknown(viewObject, typeof(UnsafeNativeMethods.IViewObject)) as
                                UnsafeNativeMethods.IViewObject;
                        //呼叫Draw方法 
                        if (o != null)
                            o.Draw((int)DVASPECT.DVASPECT_CONTENT,
                                -1,
                                IntPtr.Zero,
                                null,
                                IntPtr.Zero,
                                image.GetHdc(),
                                new NativeMethods.Comrect(bmpRect),
                                null,
                                IntPtr.Zero,
                                0);
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine(ex.Message);
                        throw;
                    }
                    //釋放 
                    image.Dispose();
                    return bitmap;
                }
            }


            [SuppressUnmanagedCodeSecurity]
            internal static class UnsafeNativeMethods
            {
                public static Guid IidIViewObject = new Guid("{0000010d-0000-0000-C000-000000000046}");


                [ComImport, Guid("0000010d-0000-0000-C000-000000000046"),
                 InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
                public interface IViewObject
                {
                    [PreserveSig]
                    int Draw([In, MarshalAs(UnmanagedType.U4)] int dwDrawAspect, int lindex, IntPtr pvAspect,
                        [In] NativeMethods.TagDvtargetdevice ptd, IntPtr hdcTargetDev, IntPtr hdcDraw,
                        [In] NativeMethods.Comrect lprcBounds, [In] NativeMethods.Comrect lprcWBounds,
                        IntPtr pfnContinue,
                        [In] int dwContinue);


                    [PreserveSig]
                    int GetColorSet([In, MarshalAs(UnmanagedType.U4)] int dwDrawAspect, int lindex, IntPtr pvAspect,
                        [In] NativeMethods.TagDvtargetdevice ptd, IntPtr hicTargetDev,
                        [Out] NativeMethods.TagLogpalette ppColorSet);


                    [PreserveSig]
                    int Freeze([In, MarshalAs(UnmanagedType.U4)] int dwDrawAspect, int lindex, IntPtr pvAspect,
                        [Out] IntPtr pdwFreeze);


                    [PreserveSig]
                    int Unfreeze([In, MarshalAs(UnmanagedType.U4)] int dwFreeze);


                    void SetAdvise([In, MarshalAs(UnmanagedType.U4)] int aspects,
                        [In, MarshalAs(UnmanagedType.U4)] int advf,
                        [In, MarshalAs(UnmanagedType.Interface)] IAdviseSink pAdvSink);


                    void GetAdvise([In, Out, MarshalAs(UnmanagedType.LPArray)] int[] paspects,
                        [In, Out, MarshalAs(UnmanagedType.LPArray)] int[] advf,
                        [In, Out, MarshalAs(UnmanagedType.LPArray)] IAdviseSink[] pAdvSink);
                }
            }
        }
    }
}
 

使用：

string url = Request.Url.ToString();
              	string savePath = Server.MapPath("~\\images\\") + Guid.NewGuid().ToString()+".png";
          	  ImageHelper.SaveUrlToImage(url, savePath, ImageType.PNG);

Tips：

原網頁頁簽上加 AspCompat="true"