C# console app to set the top-most picture on a subreddit to the Windows lock screen

Program.cs

using System;
using System.IO;
using System.Net;
using System.Runtime.InteropServices;
using Microsoft.Win32;
using Newtonsoft.Json.Linq;

namespace SubredditLockscreen
{
    class Program
    {
        /* ====================================================
         * 
         * !! MUST BE RUN AS ADMIN !!
         * (Also requires a reference to Newtonsoft.Json)
         * 
         * USAGE:
         *   SubredditLockscreen.exe /r/EarthPorn
         *   SubredditLockscreen.exe r/NaturePics/hot
         * ====================================================
         */
        static void Main(string[] args)
        {
            string subredditArg = args[0];
            if (!subredditArg.Contains("reddit.com"))
            {
                subredditArg = $"https://reddit.com{(subredditArg.StartsWith("/") ? "" : "/")}{subredditArg}";
            }

            if (!subredditArg.EndsWith(".json"))
            {
                subredditArg += ".json";
            }

            string imageUrl = GetLatestImgPostFromSubreddit(subredditArg);
            bool success = SetLockScreen(imageUrl);
            if (success)
                Console.WriteLine("Lockscreen image set!");
        }

        private static string GetLatestImgPostFromSubreddit(string subredditUrl)
        {
            JToken json;
            using (WebClient client = new WebClient())
            {
                json = JToken.Parse(client.DownloadString(subredditUrl));
            }

            JArray posts = json["data"]["children"] as JArray;
            foreach (JObject post in posts)
            {
                JToken postInfo = post["data"];
                bool isSelfPost = postInfo["is_self"].Value<bool>();
                string thumbnail = postInfo["thumbnail"].Value<string>();

                if (!isSelfPost && thumbnail != "default")
                {
                    string url = postInfo["url"].Value<string>();
                    return url;
                }
            }

            return "";
        }

        [DllImport("kernel32.dll", SetLastError = true)]
        public static extern bool Wow64DisableWow64FsRedirection(ref IntPtr ptr); //If on 64 bit, C# will replace "System32" with "SysWOW64". This disables that.

        private static bool SetLockScreen(string imageUrl)
        {
            try
            {
                IntPtr ptr = new IntPtr();
                Wow64DisableWow64FsRedirection(ref ptr);

                const string REGISTRY_KEY = @"HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\PersonalizationCSP";
                const string LOCK_SCREEN_DEST_PATH = @"C:\Windows\System32\LockScreen.jpg";

                if (File.Exists(LOCK_SCREEN_DEST_PATH))
                {
                    File.Delete(LOCK_SCREEN_DEST_PATH);
                }

                using (WebClient client = new WebClient())
                {
                    client.DownloadFile(imageUrl, LOCK_SCREEN_DEST_PATH);
                }

                Registry.SetValue(REGISTRY_KEY, "LockScreenImageStatus", 1, RegistryValueKind.DWord);
                Registry.SetValue(REGISTRY_KEY, "LockScreenImagePath", LOCK_SCREEN_DEST_PATH, RegistryValueKind.String);
                Registry.SetValue(REGISTRY_KEY, "LockScreenImageUrl", LOCK_SCREEN_DEST_PATH, RegistryValueKind.String);
            }
            catch
            {
                return false;
            }

            return true;
        }
    }
}