All functions can be found in themes/sample/theme.php. Everytime you need to change something just copy the function you need in themes/your_theme_name/theme.php.
You can use function $template_display_media:
/******************************************************************************
** Section <<<$template_display_media>>> - START
******************************************************************************/
// HTML template for intermediate image display
$template_display_media = <<<EOT
<tr>
<td align="center" class="display_media" nowrap="nowrap">
<table width="100%" cellspacing="2" cellpadding="0">
<tr>
<td align="center" style="{SLIDESHOW_STYLE}">
{IMAGE}
</td>
</tr>
</table>
</td>
</tr>
<tr>
<td>
<table width="100%" cellspacing="2" cellpadding="0" class="tableb tableb_alternate">
<tr>
<td align="center">
{ADMIN_MENU}
</td>
</tr>
</table>
<!-- BEGIN img_desc -->
<table cellpadding="0" cellspacing="0" class="tableb tableb_alternate" width="100%">
<!-- BEGIN title -->
<tr>
<td class="tableb tableb_alternate"><h1 class="pic_title">
{TITLE}
</h1></td>
</tr>
<!-- END title -->
<!-- BEGIN caption -->
<tr>
<td class="tableb tableb_alternate"><h2 class="pic_caption">
{CAPTION}
</h2></td>
</tr>
<!-- END caption -->
</table>
<!-- END img_desc -->
</td>
</tr>
EOT;
/******************************************************************************
** Section <<<$template_display_media>>> - END
******************************************************************************/
Paste the above code to themes/your_theme_name/theme.php and add under token {IMAGE} (or {CAPTION} or {TITLE} depends or you want it):
<p align="right">Click image to view full size<p>
Add to your themes/your_theme_name/your_style.css:
.display_media .image {
cursor: zoom-in;
cursor:-webkit-zoom-in;
}
CSS cursor Property
http://www.w3schools.com/cssref/pr_class_cursor.aspI think the zoom property does not work in all the browsers;