NextGEN Gallery 2.0.40. – set caption width

I’m using NextGEN Gallery by Photocrati Version 2.0.40. (FREE)
I’d like to create a thumbnail gallery with captions below every image.

I use this code inside the page where I want to show my thumbnail gallery:
[nggallery id=01 template=caption]

I have a problem with the caption size.
I would like to set a caption width depending to the image width.
My thumbs are not cropped, their height is fixed to 200px width.
The captions are quite long and there is no limit to their width.
This creates very ugly white spaces between each thumbnails.

How can I set a caption width depending by the thumbnail width?

Here you can see my gallery

http://wordpress.org/plugins/nextgen-gallery/