string strResult = string.Empty;
//dr["Photo"]即为从数据库读取到datatable中的image字段
                if (!string.IsNullOrEmpty(dr["Photo"].ToString()))
                {
                    byte[] photo = (byte[])dr["Photo"];
                    if (photo.Length > 0)
                    {
                        for (int i = 0; i < photo.Length; i++)
                        {
                            strResult = byteToHexStr(photo);
                        }
                    }
                }

//byte[]转16进制
public static string byteToHexStr(byte[] bytes)
        {
            StringBuilder sb = new StringBuilder();
            if (bytes != null)
            {
                for (int i = 0; i < bytes.Length; i++)
                {
                    sb.Append(bytes[i].ToString("X2"));
                }
            }
            return sb.ToString();
        }