Hi,
To add value in the alt and title tags, you can add the desired value at the end of this line:
echo $this->image->display(@$this->row->file_path,false,$this->escape($this->row->file_name), '' , '' , $this->image->main_thumbnail_x, $this->image->main_thumbnail_y);
in the view "category / listing_img_title" via the menu Display > View.
You can display for example the category name with that code:
echo $this->image->display(@$this->row->file_path,false,$this->escape($this->row->file_name), '' , '' , $this->image->main_thumbnail_x, $this->image->main_thumbnail_y,$this->row->category_name);