public string ImageToBase64String(Image imageData, ImageFormat format)  
{  
string base64;  
MemoryStream memory = new MemoryStream();  
imageData.Save(memory, format);  
base64 = System.Convert.ToBase64String(memory.ToArray());  
memory.Close();  
memory = null;  
return base64;  
}  
或  
System.IO.MemoryStream m = new System.IO.MemoryStream();  
System.Drawing.Bitmap bp = new System.Drawing.Bitmap(@“c:/a.GIF”);  
bp.Save(m, System.Drawing.Imaging.ImageFormat.Gif);  
byte[]b= m.GetBuffer();  
string base64string=Convert.ToBase64String(b);  

byte[] bt = Convert.FromBase64String(base64string);  
System.IO.MemoryStream stream = new System.IO.MemoryStream(bt);  
Bitmap bitmap = new Bitmap(stream);  
pictureBox1.Image = bitmap;

string s= "";
byte[] b = Convert.FromBase64String(s);
Response.ClearContent();
Response.AddHeader("Content-Type","image/gif");
Response.BinaryWrite(b);
Response.End();       byte[] b = (byte[])(二进制数据); pic.Image = Image.FromStream(new MemoryStream(b)); picData = b;