I have links to images on my website (fined with lightbox),
when I extend the links with
rel="lightbox nofollow" would this increase the link juice value of the other links? I don't need all of the images indexed, a few of em.
It is not advisable to
As pointed out in the comments, by nofollowing internal links on your website, this no longer causes more PageRank to flow via the followable links.
This illustration from Moz demonstrates how PageRank flows pretty well:-
And to cite a snippet from this article:-
Thanks to @Binarysurf for the clarification of this.
It's not recommended to use
Why blocking your images? It's better if all of your content (pages, images, video, etc.) are indexed, every single item might be another door for letting visitors get into your site.