base64 encode HttpPostedFileBase

I tried this and it worked

string theFileName = Path.GetFileName(YourFile.FileName);
byte[] thePictureAsBytes = new byte[YourFile.ContentLength];
using (BinaryReader theReader = new BinaryReader(YourFile.InputStream))
{
    thePictureAsBytes = theReader.ReadBytes(YourFile.ContentLength);
}
string thePictureDataAsString = Convert.ToBase64String(thePictureAsBytes);