Read my previous post.

You can use this method from Page_Load in the following manner (if you want the ASPX page to return an image).

public partial class Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        MemoryStream mem = TransparentGif.DrawTransparentGif(
            "Test", Color.Red, 128, 128);
        Response.Clear();
        Response.BufferOutput = true;
        Response.ContentType = "image/gif";
        Response.BinaryWrite(mem.ToArray());
        Response.Flush();
        return;
    }
}