I dont think it is defined in global for use in php..
so you have to define it yourself,
maybe if using costum images for your mod, create your own img folder
sub inside the /images/modcostumimagesfolder/
and remember to add a blank index.html file.
Its easy to define in your script..
here is the test i just did to check if stylevar is defined in global.
PHP Code:
<?php
require_once('./global.php');
// set fixed defs
$folder = $stylevar['imgdir_misc'];
$misc_folder = './images/misc/';
$img = 'calendar.gif';
// echo's + test
echo 'hello <br />';
echo 'Folder name : ';
echo $folder . '<br />';
echo 'Image name : ';
echo $folder . $img .'<br />';
echo '<img src="'. $folder . $img .'" /> <br />';
echo '-------- <br />';
echo 'Folder 2 name : ';
echo $misc_folder . '<br />';
echo '<img src="'. $misc_folder . $img .'" />';
?>