n3k4

To help your WordPress installation be more optimized for search engines, this plugin will include a ‘noindex’ meta tag in the header of any duplicate posts. 
Robots will not index any posts with matching title tags, which is a known indicator of negative SEO. This is very useful for automated posting and working with a large amount of posts.

Noindex Duplicate Posts

This plugin will automatically add a 'Noindex' meta tag to posts that are a duplicate determined by the slug and preexisting post names.

modernwebstudios

This plugin add meta tag noindex,nofolow to head of any attachment page().

MWS Noindex Attachment Pages

This plugin add meta tag noindex,nofolow to head of any attachment page().

Noindex Duplicate Posts vs MWS Noindex Attachment Pages