hello and welcome to 4images forum
...
less information for thumbnail / image only on index page (not on category page) ...
... try this ...
1.1 in index.php find the following code line
$templates_used = 'home,category_bit,whos_online,thumbnail_bit';
and replace it by
$templates_used = 'home,category_bit,whos_online,thumbnail_index_bit';
1.2. in index.php find the following code line
$new_images .= $site_template->parse_template("thumbnail_bit");
and replace it by
$new_images .= $site_template->parse_template("thumbnail_index_bit");
2.1 make a copy of your /templates/<your_template>/thumbnail_bit.html and rename it to thumbnail_index_bit.html
2.2 in your new /templates/<your_template>/thumbnail_index_bit.html delete all the informations you won't show with your thumbnails on index page e.g. ...
<a href="{cat_url}">{cat_name}</a><br />
{if allow_comments}{lang_comments} {image_comments}{endif allow_comments}<br />
{lightbox_button}<br>
{download_button}
... I think ... that's all ...