Images, Greyscale and Joomlapolis

All,

I don't know how to do it, but when I checked php.net/manual/en/function.imagefilter.php I came across the following php code for presenting images in greyscale:

<?php
$image = imagecreatefrompng('nathalie.png');

imagefilter($image, IMG_FILTER_GRAYSCALE);

imagepng($image, 'img_filter_grayscale.png');

imagedestroy($image);
?>

Would there be a way to integrate the above code with the Joomlapolis CB login (as a plugin?) so that site visitors would only see images in greyscale, yet logged in members would be able to see images in full colour?

Appreciate any suggestions.

Sincerely,
Customs