Try this method.
cn.Open();
SqlCommand cmd = new SqlCommand("SELECT * FROM ImageUpload WHERE ImgID='100'",cn);
SqlDataReader dr = cmd.ExecuteReader();
if (dr.Read())
{
string image = Convert.ToString(DateTime.Now.ToFileTime());
byte[] bimage = (byte[])dr["ImgData"];
FileStream fs = new FileStream(image, FileMode.CreateNew, FileAccess.Write);
fs.Write(bimage, 0, bimage.Length - 1);
fs.Close();
pictureBox1.Image = Image.FromFile(image);
}
dr.Close();
cn.Close();