Image image = Image.FromFile(@"C:\Users\swkj\Documents\Visual Studio 2012\Projects\WebApplication9\WindowsFormsApplication1\ali.jpg");//这是你图片文件的

MemoryStream stream = new MemoryStream();

image.Save(stream, ImageFormat.Bmp); //把图片保存到流中。

byte[] b = stream.ToArray();

string i = string.Empty;

//foreach (var a in b)

//{

// i += a;

//}

string a = Convert.ToBase64String(b);  //base64加密