api图片传输，转成64位字符串进行传输

byte[] getImageByte = HttpHelper.getImageByte(HttpContext.Current.Server.MapPath(("~/UploadFiles/StuImgs/" + result_Model.StuImage)));
if (getImageByte != null)
{
student.StuImage = result_Model.StuImage;
student.pic_data = Convert.ToBase64String(getImageByte);
}
else
{
student.StuImage = "";//图片找不到
}