对网页所有的图片加水印的方式有 2 种：
Html 页面：
<body>
<!-- 图片 src 属性请求了一个服务器端的一般处理程序 -->
<img src="AddWaterMarkDynamic.ashx?name=sky11.jpg" alt="" />
</body>
一般处理程序：
public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "image/jpeg";
string msg = "Hello World!";
string imgName = context.Request.QueryString["name"];
if (!string.IsNullOrEmpty(imgName))
{
string imgPath = context.Server.MapPath("upload/image/" + imgName);
using (Image img = Bitmap.FromFile(imgPath))
{
// 创建一个绘图者，并指定绘制图像
using (Graphics g = Graphics.FromImage(img))
{
g.DrawString(msg, new Font("Verdana", 12, FontStyle.Bold), Brushes.Black, new PointF(5, 8));
img.Save(context.Response.OutputStream, ImageFormat.Jpeg);
}
}
}
}
效果：
public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "image/jpeg";
string msg = "Hello World!";
string imgName = context.Request.QueryString["name"];
if (!string.IsNullOrEmpty(imgName))
{
string imgPath = context.Server.MapPath("upload/image/" + imgName);
using (Image img = Bitmap.FromFile(imgPath))
{
string water = context.Server.MapPath("upload/image/water.jpg");
using (Image waterImg = Image.FromFile(water))
{
using (Graphics g = Graphics.FromImage(img))
{
g.DrawImage(waterImg, (img.Width - waterImg.Width) / 2, (img.Height - waterImg.Height) / 2);
img.Save(context.Response.OutputStream, ImageFormat.Jpeg);
}
}
}
}
}
此示例很简单，可优化的部分有很多，比如重构成一个水印工厂类，来做到精确控制水印内容、位置、文字水印还是图片水印、透明度等等。
在接收到用户上传后的文件，如果文件类型是图片类型，你在保存原图的同时可能还需要保存一张缩略图。
public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "text/html";
HttpPostedFile file = context.Request.Files[0];
if (file.ContentLength > 0)
{
string extName = Path.GetExtension(file.FileName);
string fileName = Guid.NewGuid().ToString();
string fullName = fileName + extName;
string phyFilePath = context.Server.MapPath("~/Upload/Image/") + fullName;
file.SaveAs(phyFilePath);
context.Response.Write("上传成功！文件名：" + fullName + "<br />");
if (file.ContentType.Contains("image"))
{
context.Response.Write(string.Format("<img src=‘Upload/Image/{0}‘/><br />", fullName));
using (Image img = Bitmap.FromStream(file.InputStream))
{
using (Bitmap smallImg = new Bitmap(120, 40))
{
using (Graphics g = Graphics.FromImage(smallImg))
{
g.DrawImage(img, new Rectangle(0, 0, smallImg.Width, smallImg.Height),
new Rectangle(0, 0, img.Width, img.Height), GraphicsUnit.Pixel);
smallImg.Save(context.Server.MapPath("~/Upload/Image/") + fileName + "_small" + extName);
context.Response.Write(string.Format("缩略图保存成功！<br />"));
context.Response.Write(string.Format("<img src=‘Upload/Image/{0}‘/><br />", (fileName + "_small" + extName)));
}
}
}
}
}
}
原文：http://www.cnblogs.com/SkySoot/p/3525700.html