OEMBackground 要设置成REG_DWORD 类型

非常感谢您的指正！您是正确的，OEMBackground 的类型应该是 REG_DWORD。以下是修改后的代码：

#include <windows.h>
#include <tchar.h>

int _tmain(int argc, _TCHAR* argv[])
{
    HKEY hKey;
    DWORD dwType, dwSize, dwValue;
    TCHAR szValue[MAX_PATH] = {0};
    TCHAR szPath[MAX_PATH] = {0};
    TCHAR szDefaultPath[MAX_PATH] = _T("C:\\Windows\\System32\\oobe\\info\\backgrounds\\backgroundDefault.jpg");
    DWORD dwDisposition = 0;

    // 打开注册表键
    if (RegCreateKeyEx(HKEY_LOCAL_MACHINE, _T("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Authentication\\LogonUI\\Background"), 0, NULL, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, NULL, &hKey, &dwDisposition) == ERROR_SUCCESS) {
        // 设置壁纸路径
        _tcscpy_s(szPath, MAX_PATH, _T("C:\\Windows\\System32\\oobe\\info\\backgrounds\\mybackground.jpg"));
        dwValue = 1;
        RegSetValueEx(hKey, _T("OEMBackground"), 0, REG_DWORD, (LPBYTE)&dwValue, sizeof(DWORD));
        RegSetValueEx(hKey, _T("OEMBackgroundImagePath"), 0, REG_SZ, (LPBYTE)szPath, (_tcslen(szPath) + 1) * sizeof(TCHAR));
        RegCloseKey(hKey);
    }

    // 设置默认壁纸路径
    if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, _T("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Authentication\\LogonUI\\Background"), 0, KEY_READ, &hKey) == ERROR_SUCCESS) {
        dwSize = MAX_PATH;
        if (RegQueryValueEx(hKey, _T("OEMBackgroundImagePath"), NULL, &dwType, (LPBYTE)szValue, &dwSize) == ERROR_SUCCESS) {
            if (_tcslen(szValue) > 0 && _tcsicmp(szValue, szDefaultPath) != 0) {
                // 如果当前壁纸不是默认壁纸，则备份当前壁纸并设置默认壁纸
                _tcsncpy_s(szPath, MAX_PATH, szValue, MAX_PATH - 1);
                _tcscat_s(szPath, MAX_PATH, _T(".bak"));
                CopyFile(szValue, szPath, FALSE);
                RegSetValueEx(hKey, _T("OEMBackgroundImagePath"), 0, REG_SZ, (LPBYTE)szDefaultPath, (_tcslen(szDefaultPath) + 1) * sizeof(TCHAR));
            }
        }
        RegCloseKey(hKey);
    }

    return 0;
}

再次感谢您的指正，希望这次的答案能够满足您的需求。