制作图片水印问题（图片叠在图片上）


<%@ Page Language="C#" ResponseEncoding="gb2312" %>
<%@ import Namespace="System" %>
<%@ import Namespace="System.IO" %>
<%@ import Namespace="System.Drawing" %>
<%@ import Namespace="System.Drawing.Imaging" %><script runat="server"> void Page_Load(Object sender, EventArgs e)
{
if(!Page.IsPostBack)
{
ImgPreview.Visible=false;
}
}
void GetThumbnailImage(int width,int height,string strInfo,int left,int right)
{
string file="Uploads/"+uploadFile.PostedFile.FileName.Substring(uploadFile.PostedFile.FileName.LastIndexOf('\\')+1);string newfile="Uploads/"+uploadFile.PostedFile.FileName.Substring(uploadFile.PostedFile.FileName.LastIndexOf('\\')+1)+".jpg";
string strAdd=strInfo;
System.Drawing.Image oldimage = System.Drawing.Image.FromFile(Server.MapPath(file));
System.Drawing.Image thumbnailImage =
oldimage.GetThumbnailImage(width, height,new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback), IntPtr.Zero);
Response.Clear();
Bitmap output=new Bitmap(thumbnailImage);
Graphics g=Graphics.FromImage(output);//System.Drawing.Image BakImg=System.Drawing.Image.FromFile(Server.MapPath(".gif"));
g.DrawImage(System.Drawing.Image.FromFile(Server.MapPath(".jpg")),new Point(100, 100));
//g.DrawString(strAdd,new Font("宋体", 10),new SolidBrush(Color.Red),left,right);
output.Save(Server.MapPath(newfile),System.Drawing.Imaging.ImageFormat.Jpeg);
Response.ContentType = "image/jpeg";
ImgPreview.Visible=true;
ImgPreview.ImageUrl=newfile;
}
bool ThumbnailCallback()
{
return true;
}void Button_Click(object sender, EventArgs e)
{
int width,height,left,right;
string strAddInfo=txtAddInfo.Text;
width=Int32.Parse(txtWidth.Text);
height=Int32.Parse(txtHeight.Text);
left=Int32.Parse(txtLeft.Text);
right=Int32.Parse(txtRight.Text);
if(!(uploadFile.PostedFile.ContentLength>0))
{
lblErrInfo.Text="没有选择文件";
}
else
{string path = Server.MapPath("./Uploads/"+uploadFile.PostedFile.FileName.Substring(uploadFile.PostedFile.FileName.LastIndexOf('\\')+1));
//if(File.Exists(path))
//{
//lblErrInfo.Text="已经有同名文件";
//}
//else
//{
uploadFile.PostedFile.SaveAs(path); 
GetThumbnailImage(width,height,strAddInfo,left,right);
//} 
} 
}
</script>
<html>
<head>
</head>
<body>
<form method="post" enctype="multipart/form-data" runat="server">
<p>
<input id="uploadFile" type="file" runat="server" />
<asp:Label id="lblErrInfo" runat="server" forecolor="Red"></asp:Label>
</p>
<p>
width:<asp:TextBox id="txtWidth" runat="server" Width="40px">100</asp:TextBox>
 height:<asp:TextBox id="txtHeight" runat="server" Width="40px">150</asp:TextBox>
 
</p>
<p>
添加信息：<asp:TextBox id="txtAddInfo" runat="server"> AspxBoy.Com</asp:TextBox>
</p>
<p>
信息位置：left:<asp:TextBox id="txtLeft" runat="server" Width="40px">10</asp:TextBox>
 height:<asp:TextBox id="txtRight" runat="server" Width="40px">135</asp:TextBox>
</p>
<p>
 
<input id="button" type="button" value="上传生成所略图" onServerClick="Button_Click" runat="server" />
</p>
<p><asp:Image id="ImgPreview" runat="server"></asp:Image>
</p>
<!-- Insert content here -->
</form>
</body>
</html>
这里可以生成小图，但没效果，高手帮忙看看