I want to take a screenshot of an external website. Currently my workflow is to start a Firefox instance with the specified URL and take a screenshot using PrintWindow in the Win32 API

When I run this application in IISExpress it works fine but when I run the same application in IIS on a windows VPS it is not working (screenshot is blank).

I don't know what I'm doing wrong?

My code:

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Drawing;
using System.Drawing.Imaging;
using System.Linq;
using System.Runtime.InteropServices;
using System.Security;
using System.Threading;
using System.Web;

namespace WebTools.Web
{
    public class RemoteScreenshot
    {
        public static Bitmap TakeScreenshot(Process process)
        {
            // may need a process Refresh before
            return TakeScreenshot(process.MainWindowHandle);
        }

        public static Bitmap TakeScreenshot(IntPtr handle)
        {
            RECT rc = new RECT();
            GetWindowRect(handle, ref rc);

            Bitmap bitmap = new Bitmap(rc.right - rc.left, rc.bottom - rc.top);

            using (Graphics graphics = Graphics.FromImage(bitmap))
            {
                PrintWindow(handle, graphics.GetHdc(), 0);
            }

            return bitmap;
        }

        [DllImport("user32.dll")]
        private static extern bool GetWindowRect(IntPtr hWnd, ref RECT rect);

        [DllImport("user32.dll")]
        private static extern bool PrintWindow(IntPtr hWnd, IntPtr hDC, int flags);

        [StructLayout(LayoutKind.Sequential)]
        private struct RECT
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
        }

        public static void Save(string url, string file, int timeout = 0)
        {
            Process.Start(new ProcessStartInfo("C:\\Program Files (x86)\\Mozilla Firefox\\firefox.exe", url)
            {
                CreateNoWindow = false,
                WindowStyle = ProcessWindowStyle.Maximized
            });

            Thread.Sleep(timeout);

            var bitmap = TakeScreenshot(Process.GetProcessesByName("firefox").First());

            bitmap.Save(file, ImageFormat.Png);
            bitmap.Dispose();

            Process.GetProcessesByName("firefox").First().Kill();
        }
    }
}

EDIT: Running Firefox works fine because the AppPool is under another account that has the rights to execute firefox.