The customized web-page must have the file name netlogin_login_page.html.
<img src="netlogin_<xxx>.jpg"> or
<img src="netlogin_<xxx>.jpeg"> or
<img src="<netlogin_<xxx>.gif">
where <xxx> is user-configurable.
The following is a sample custom page, where the embedded graphical image is named netlogin_welcome.jpg:
<html lang="en"> <head> <title>Network Login Page</title> </head> <body> <form action="/hello" method="post"> <img src="netlogin_welcome.jpg"> <br/> Please log in: <br/> User: <input type="text" name="extremenetloginuser" /> <br/> Password: <input type="password" name="extremenetloginpassword" /> <br/> <input type="submit" value="Submit" /> </form> </body> </html>