Change images on the site – not in the admin area

hey guys, i have a general question, how this could be archieved…
not sure if this is the right forum (would post it to wp-advanced, but can′t post there).
i have a page with static images. this images should be changeable by the user. the user should log in, go to the page and be able to change an image(e.g. pressing an icon connected with the image). then he would just paste the new image src link in a popup and the new images should then be changed and saved.
atm:

<div id="pageContactLeftBox">
	<img src="<?php bloginfo('template_directory'); ?>/images/kon1.jpg" class="imgDeco imgHomeBig">
</div>

could somebody give some tipps???
thanks.