You should be showing your pics in order after the first randomization. I noticed several pics being faded out only to show up again next...
This is the code (1st image is random, then the "normal" order):
<div id="slider">
<ul id="sliderContent">
<?php
$header = array(
array('http://virgilio.lorenzoraffio.com/wp-content/themes/virgilio/images/header/aula_magna.jpg', 'CAPTION AULA MAGNA', 'right'),
array('http://virgilio.lorenzoraffio.com/wp-content/themes/virgilio/images/header/portone.jpg', 'CAPTION PORTONE', 'bottom'),
array('http://virgilio.lorenzoraffio.com/wp-content/themes/virgilio/images/labchimica.jpg', 'CAPTION LAB CHIMICA', 'top'),
array('http://virgilio.lorenzoraffio.com/wp-content/themes/virgilio/images/header/aula_informatica.jpg', 'CAPTION INFORMATICA', 'bottom'),
array('http://virgilio.lorenzoraffio.com/wp-content/themes/virgilio/images/header/atrio.jpg', 'CAPTION ATRIO', 'top'),
);
$rand = rand(0, count($header) - 1);
echo '<li class="sliderImage"><img src="', $header[$rand][0], '" width="', HEADER_IMAGE_WIDTH, '" height="', HEADER_IMAGE_HEIGHT, '" alt="" /><span class="', $header[$rand][2], '">', $header[$rand][1], '</span></li>'; ?>
<li class="sliderImage">
<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/header/aula_magna.jpg" width="<?php echo HEADER_IMAGE_WIDTH; ?>" height="<?php echo HEADER_IMAGE_HEIGHT; ?>" alt="" />
<span class="right"><strong>L'aula magna</strong><br />CAPTION AULA MAGNA</span>
</li>
<li class="sliderImage">
<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/header/portone.jpg" width="<?php echo HEADER_IMAGE_WIDTH; ?>" height="<?php echo HEADER_IMAGE_HEIGHT; ?>" alt="" />
<span class="bottom"><strong>Il portone</strong><br />CAPTION PORTONE</span>
</li>
<li class="sliderImage">
<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/header/aula_informatica.jpg" width="<?php echo HEADER_IMAGE_WIDTH; ?>" height="<?php echo HEADER_IMAGE_HEIGHT; ?>" alt="" />
<span class="top"><strong>Laboratorio di Chimica</strong><br />CAPTION LAB CHIMICA</span>
</li>
<li class="sliderImage">
<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/labfisica.jpg" width="<?php echo HEADER_IMAGE_WIDTH; ?>" height="<?php echo HEADER_IMAGE_HEIGHT; ?>" alt="" />
<span class="top"><strong>Laboratorio di Fisica</strong><br />CAPTION INFORMATICA</span>
</li>
<li class="sliderImage">
<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/header/atrio.jpg" width="<?php echo HEADER_IMAGE_WIDTH; ?>" height="<?php echo HEADER_IMAGE_HEIGHT; ?>" alt="" />
<span class="top"><strong>Atrio</strong><br />CAPTION ATRIO</span>
</li>
<li class="sliderImage">
</li>
</ul>
</div>If the 1st (random) image is "Aula magna", the non-random list have still "Aula magna" as the 1st item.. So I'll have again the same slides one after the other..