//图片转为base64编码的字符串
		protected string ImgToBase64String(string Imagefilename)
		{
			try
			{
				Bitmap bmp = new Bitmap(Imagefilename);
				MemoryStream ms = new MemoryStream();
				bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
				byte[] arr = new byte[ms.Length];
				ms.Position = 0;
				ms.Read(arr, 0, (int)ms.Length);
				ms.Close();
				return Convert.ToBase64String(arr);
			}
			catch (Exception ex)
			{
				return null;
			}
		}

		//threeebase64编码的字符串转为图片
		protected Bitmap Base64StringToImage(string strbase64)
		{
			try
			{
				byte[] arr = Convert.FromBase64String(strbase64);
				MemoryStream ms = new MemoryStream(arr);
				Bitmap bmp = new Bitmap(ms);

				 bmp.Save(@"d:\test.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);
				//bmp.Save(@"d:\"test.bmp", ImageFormat.Bmp);
				//bmp.Save(@"d:\"test.gif", ImageFormat.Gif);
				//bmp.Save(@"d:\"test.png", ImageFormat.Png);
				ms.Close();
				return bmp;
			}
			catch (Exception ex)
			{
				return null;
			}
		}

//图片转为base64编码的字符串
		protected string ImgToBase64String(string Imagefilename)
		{
			try
			{
				Bitmap bmp = new Bitmap(Imagefilename);

				MemoryStream ms = new MemoryStream();
				bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
				byte[] arr = new byte[ms.Length];
				ms.Position = 0;
				ms.Read(arr, 0, (int)ms.Length);
				ms.Close();
				return Convert.ToBase64String(arr);
			}
			catch (Exception ex)
			{
				return null;
			}
		}

		//threeebase64编码的字符串转为图片
		protected Bitmap Base64StringToImage(string strbase64)
		{
			try
			{
				byte[] arr = Convert.FromBase64String(strbase64);
				MemoryStream ms = new MemoryStream(arr);
				Bitmap bmp = new Bitmap(ms);

				 bmp.Save(@"d:\test.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);
				//bmp.Save(@"d:\"test.bmp", ImageFormat.Bmp);
				//bmp.Save(@"d:\"test.gif", ImageFormat.Gif);
				//bmp.Save(@"d:\"test.png", ImageFormat.Png);
				ms.Close();
				return bmp;
			}
			catch (Exception ex)
			{
				return null;
			}
		}
            //2: 图片直接显示
            string Base64String = "";//太长就不贴出来了
            byte[] bytes = Convert.FromBase64String(Base64String);
            ImageTagId.ImageUrl = "data:image/jpeg;base64," + Convert.ToBase64String(bytes);//

//    
public System.Drawing.Image Base64ToImage(string base64String)
        {
            byte[] imageBytes = Convert.FromBase64String(base64String);
            MemoryStream ms = new MemoryStream(imageBytes, 0, imageBytes.Length);
            ms.Write(imageBytes, 0, imageBytes.Length);
            System.Drawing.Image image = System.Drawing.Image.FromStream(ms, true);
            return image;
        }

使用方法：

    Base64ToImage(dd).Save(Server.MapPath("Hello.jpg"));
   Image1.ImageUrl = "Hello.jpg";;


//4：转换成图片另存为然后图片显示出来
string dd = "";//太长就不贴出来了

            var bytes = Convert.FromBase64String(dd);
            using (var imageFile = new FileStream(@"d:\Hello1.jpg", FileMode.Create))
            {
                imageFile.Write(bytes, 0, bytes.Length);
                imageFile.Flush();
            }
//5://直接转换存为路径下图片
string base64Str=""/  
  
e[] bytes = System.Convert.FromBase64String(dd);  
  
       File.WriteAllBytes(@"d:\newfile.jpg", bytes);  
 string filePath = @"d:\MyImage.jpg";  
  File.WriteAllBytes(filePath, Convert.FromBase64String(base64Str));  

6：多张base64图片转换为图片另存为
public string Base64ToImage(string upimgPath, string base64String)  
    {  
      string goodspath = Server.MapPath(upimgPath);  //用来生成文件夹  
      if (!Directory.Exists(goodspath))  
      {  
        Directory.CreateDirectory(goodspath);  
      }  
      var imgPath = string.Empty;  
      if (!string.IsNullOrEmpty(base64String))  
      {  
        var splitBase = base64String.Split(new char[] { ';' }, StringSplitOptions.RemoveEmptyEntries);  
        foreach (var item in splitBase)  
        {  
          var path = upimgPath + Guid.NewGuid() + ".jpg";  
  
          string filePath = Server.MapPath(path);// Server.MapPath(upimgPath + Guid.NewGuid() + ".jpg");  
          File.WriteAllBytes(filePath, Convert.FromBase64String(item));  
          imgPath += path + ";";  
        }  
      }  
      else { imgPath = ";"; }  
      return imgPath.TrimEnd(';');  
    }  

使用方法:
va headimg="";
 Base64ToImage("UpLoadImg/HeadImage/", headimg)