Checking Image Size

Hi,

is there a way to check the maximum size of an item.id? I wan't to check in my Lightbox Implementation if the size of the image is smaller than the resize the lightbox is intending to use (which causes the lightbox script to hang because it cant find the specific resize).
Im'm dreaming of something like {if size($child.id) > $limit} ...

Any hint will be appreciated
CU,
Lutz

Gallery version = 2.2-svn core 1.1.15
PHP version = 5.1.4 apache2handler
Webserver = Apache/2.2.3 (Win32) DAV/2 PHP/5.1.4 mod_ssl/2.2.2 OpenSSL/0.9.8b
Database = mysql 5.0.22-log,
Theme=PGtheme,
Gallery-URL=http://lf-photodesign.de