You don't have to guild me, but here's a working solution in C#.

As a bonus, it removes the watermark.

Screenshot: http://imgur.com/gyKNWbI.png

You can download it here: http://www.filedropper.com/ciraupdater

NOTE: I don't usually use filedropper.com - I would feel a lot safer uploading it to a personal webserver, but meh.

I ran it through VirusTotal and I'm getting what looks like one false positive - a trojan that uses the wallpaper changing class that I snagged from here: http://stackoverflow.com/questions/1061678/change-desktop-wallpaper-using-code-in-net

Virustotal:

Program.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Timers;

namespace CIRAUpdater
{
    class Program
    {
        private static Timer ticky = new Timer();
        static void Main(string[] args)
        {
            Console.WriteLine("CIRA Updater by DarkTussin" + Environment.NewLine);
            ticky.Elapsed += ticky_Elapsed;
            ticky.Interval = 100000;
            ticky.Enabled = true;
            ticky_Elapsed(null, null);
            System.Windows.Forms.Application.Run();
        }

        static void ticky_Elapsed(object sender, ElapsedEventArgs e)
        {
            Console.Write("Updating...");
            Wallpaper.Set(new Uri("http://rammb.cira.colostate.edu/ramsdis/online/images/latest_hi_res/himawari-8/full_disk_ahi_true_color.jpg"),Wallpaper.Style.Centered);
            Console.WriteLine("Updated!");
        }
    }
}

Wallpaper.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using System.IO;
using System.Drawing;

namespace CIRAUpdater
{
    public sealed class Wallpaper
    {
        Wallpaper() { }

        const int SPI_SETDESKWALLPAPER = 20;
        const int SPIF_UPDATEINIFILE = 0x01;
        const int SPIF_SENDWININICHANGE = 0x02;

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        static extern int SystemParametersInfo(int uAction, int uParam, string lpvParam, int fuWinIni);

        public enum Style : int
        {
            Tiled,
            Centered,
            Stretched
        }

        public static void Set(Uri uri, Style style)
        {
            System.IO.Stream s = new System.Net.WebClient().OpenRead(uri.ToString());
            System.Drawing.Image img = System.Drawing.Image.FromStream(s);
            System.Drawing.Graphics.FromImage(img).FillRectangle(new SolidBrush(Color.Black), new Rectangle(9, 5088, 944, 405));
            string tempPath = Path.Combine(Path.GetTempPath(), "wallpaper.bmp");
            img.Save(tempPath, System.Drawing.Imaging.ImageFormat.Bmp);
            Microsoft.Win32.RegistryKey key = Microsoft.Win32.Registry.CurrentUser.OpenSubKey(@"Control Panel\Desktop", true);
            if (style == Style.Stretched)
            {
                key.SetValue(@"WallpaperStyle", 2.ToString());
                key.SetValue(@"TileWallpaper", 0.ToString());
            }

            if (style == Style.Centered)
            {
                key.SetValue(@"WallpaperStyle", 1.ToString());
                key.SetValue(@"TileWallpaper", 0.ToString());
            }

            if (style == Style.Tiled)
            {
                key.SetValue(@"WallpaperStyle", 1.ToString());
                key.SetValue(@"TileWallpaper", 1.ToString());
            }

            SystemParametersInfo(SPI_SETDESKWALLPAPER,
                0,
                tempPath,
                SPIF_UPDATEINIFILE | SPIF_SENDWININICHANGE);
        }
    }
}