Yes, you are right, its v1.7.2 that is quiet strict because of the security...
In includes/functions.php find: $description = (!empty($image_row['image_description'])) ? format_text($image_row['image_description'], 0) : REPLACE_EMPTY;
replace with: $description = (!empty($image_row['image_description'])) ? format_text($image_row['image_description'], 0, 0, 1, 1) : REPLACE_EMPTY;
This will allow BBCode in the image description (no HTML)