using (MemoryStream stream = new MemoryStream())
         {
             PictureBox pb = c as PictureBox;
             pb.Image.Save(stream, ImageFormat.Jpeg);
             byte[] by = stream.ToArray();
             string s = System.Convert.ToBase64String(by);
          }

PictureBox pb = new PictureBox();
byte[] b = System.Convert.FromBase64String(xnChild.Attributes["Image"].InnerText);
using (MemoryStream ms = new MemoryStream(b))
{
    Image myimge = Image.FromStream(ms);
    pb.Image = myimge;
    pb.BorderStyle = BorderStyle.FixedSingle;
    pb.SizeMode = PictureBoxSizeMode.StretchImage;
}