//图片转base64
string pic_path = "aa.jpg";//图片路径
FileStream file = new FileStream(pic_path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
byte[] pic_data = new byte[file.Length];
file.Read(pic_data, 0, (int)file.Length);
file.Close();
string base64_pic = Convert.ToBase64String(photo_data);
//base64转图片
byte[] pic_data = Convert.FromBase64String(base64_pic);
using (FileStream fsWrite = new FileStream(pic_path, FileMode.Append))
{
fsWrite.Write(pic_data, 0, pic_data.Length);
};