public static string GetBase64Data()

{

string path = @"C: \txt.jpg";

FileStream filestream = new FileStream(path, FileMode.Open);

byte[] bt = new byte[filestream.Length];

//调用read读取方法

filestream.Read(bt, 0, bt.Length);

string base64Str = Convert.ToBase64String(bt);

filestream.Close();

return base64Str;

}