Dynamic signature images

About

Most Internet forums allows the poster to attach a signature to their post. The signature typically contains an image. What some people have realized is that there is no rule saying that the image must be static.

Instead some crafty people have written programs that dynamically generate an image on the fly each time someone views the signature.

The classical viewer info sign

The most typical type is an image that states information about the viewer, such as their IP address, their ISP and their webbrowser.

Exploitable php code

This code writes out the viewer IP address on a white background.

 <php

 $img=imagecreate(200,100);

 $white=imagecolorallocate($img,255,255,255);

 $black=imagecolorallocate($img,0,0,0);

 imagestring($img,0,0,0,$SERVER['REMOTEADDR'],$black);


 header('Content-Type: image/png');

 imagepng($img);

 

Random image

Exploitable php code

This code redirects to a random image file

<php
$nr=rand(1,5);
header('Location: img'.$nr.'.png',false,303);

View counter

The most advanced type remembers each time it has been viewed and does something with that. The most obvious use is to just count each time the signature has been viewed.

Special statistics

It is rather simple to create an image that lists special statistics about an user, such as their performance in a game or what media they are viewing.