Outgoing links in my site, Robots.txt and Nofollow

I have a Real Estate site that generates homes with a plugin. This plugin generates the html in my site for the homes and into that html there are two types of outgoing links:

• The images which load from a third party domain


• A property tour that loads from a third party domain

Eg:
My site: www.mydomain.com
Images links: www.realestateplugin.com/image1.jpg
property tour: www.realestateplugin.com/tour1.html

I can not control the links, so I can not put a nofollow tag to each one of these links.

Do you think it is good to block the images and the property tour urls in robots.txt for google not to see so many outgoing links?

Thanks