using System;
using Microsoft.Win32;

namespace WallPaper
{
    class Program
    {
        static void Main(string[] args)
        {
            RegistryKey rk = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Themes\LastTheme");
            if (rk == null)
            {
                Console.WriteLine("不存在！");
                return;
            }
            Console.WriteLine("Wallpaper:" + rk.GetValue("Wallpaper"));
            Console.WriteLine("按Enter退出！");
            Console.ReadLine();
        }
    }
}

------解决方案--------------------
对。注册表里应该可以查到。

------解决方案--------------------
1.引入com定义
  enum   WPSTYLE 
 { 
 CENTER   =   0, 
 TILE   =   1, 
 STRETCH   =   2, 
 MAX   =   3 
 } 
   
 struct   WALLPAPEROPT 
 { 
 public   int   dwSize; 
 public   WPSTYLE   dwStyle; 
 } 
   
 struct   COMPONENTSOPT 
 { 
 public   int   dwSize; 
 [MarshalAs(UnmanagedType.Bool)]   public   bool   fEnableComponents; 
 [MarshalAs(UnmanagedType.Bool)]   public   bool   fActiveDesktop; 
 } 
   
 struct   COMPPOS 
 { 
 public   const   int   COMPONENT_TOP   =   0x3FFFFFFF; 
 public   const   int   COMPONENT_DEFAULT_LEFT   =   0xFFFF; 
 public   const   int   COMPONENT_DEFAULT_TOP   =   0xFFFF; 
   
 public   int   dwSize; 
 public   int   iLeft; 
 public   int   iTop; 
 public   int   dwWidth; 
 public   int   dwHeight; 
 public   int   izIndex; 
 [MarshalAs(UnmanagedType.Bool)]   public   bool   fCanResize; 
 [MarshalAs(UnmanagedType.Bool)]   public   bool   fCanResizeX; 
 [MarshalAs(UnmanagedType.Bool)]   public   bool   fCanResizeY; 
 public   int   iPreferredLeftPercent; 
 public   int   iPreferredTopPercent; 
 } 
   
 [Flags] 
 enum   ITEMSTATE 
 { 
 NORMAL   =   0x00000001, 
 FULLSCREEN   =   00000002, 
 SPLIT   =   0x00000004, 
 VALIDSIZESTATEBITS   =   NORMAL   |   SPLIT   |   FULLSCREEN, 
 VALIDSTATEBITS   =   NORMAL   |   SPLIT   |   FULLSCREEN   | 
 unchecked((int)0x80000000)   |   0x40000000 
 } 
   
 struct   COMPSTATEINFO 
 { 
 public   int   dwSize; 
 public   int   iLeft; 
 public   int   iTop; 
 public   int   dwWidth;