string haarXmlPath = @"../../haarcascade_frontalface_alt_tree.xml";

FileInfo file = new FileInfo(fileName);

string  fullName = file.FullName;

string haarXmlPath = @"haarcascade_frontalface_alt_tree.xml";

string fullName = Application.StartupPath.Substring(0, Application.StartupPath.LastIndexOf("http://"));

fullName = fullName.Substring(0, fullName.LastIndexOf("http://")) + "http://" + haarXmlPath;

/// <summary>
/// 獲取應用程序根路徑
/// </summary>
private static string GetApplicationPath()
{
        string path = Application.StartupPath;
        //string path=AppDomain.CurrentDomain.BaseDirectory; //另一種獲取方式
        string folderName = String.Empty;
        while (folderName.ToLower() != "bin")
        {
            path = path.Substring(0, path.LastIndexOf("http://"));
            folderName = path.Substring(path.LastIndexOf("http://") + 1);
        }
        return path.Substring(0, path.LastIndexOf("http://") + 1);
}