In HTML pages, images are typically linked rather than embedded using the

<img src="[protocol]://[url]" />

tag. If you want to embed the image data, for example to handle just a single file containing text and images, you need to replace the src attribute with the Base64-encoded binary content of the image using the data: protocol:

<img src="data:image/jpeg;base64,[data]">

To encode an image file in Base64, use the following function (originally found here):

string MakeImageSrcData(string filename)
{
  FileStream fs = new FileStream(filename, FileMode.Open, FileAccess.Read);
  byte[] filebytes = new byte[fs.Length];
  fs.Read(filebytes, 0, Convert.ToInt32(fs.Length));
  return "data:image/png;base64," +
    Convert.ToBase64String(filebytes, Base64FormattingOptions.None);
}

This function can now be used to render an image in either aspx/ascx:

<img src="<%=MakeImageSrcData("c:\path\to\my.png") %>" />

or C#

Response.Output.WriteLine("<img src=\"" + 
    MakeImageSrcData("c:\path\to\my.png") + "\"/>");

The rendering result depends on the browser, though, as Wikipedia describes:

• Firefox and Chrome render the embedded images correctly
• Internet Explorer (7 (Vista)/8 (Win7)) only renders some because of a 32kB limit
• Word 2007 only renders image placeholders

This is too bad, since I originally intended to generate WordHtml and include pictures directly in HTML.