What is duplicate content and how can I avoid being penalized for it on my site?
I have a nature photography site with multiple types of photo galleries. Each photo and associated caption on my site appears in several galleries. For instance, a photo of a goldfinch that was taken on a trip to New Mexico in 2008 will appear in the "goldfinch.php" gallery, in the "finches.php" gallery, and in the "New_Mexico_2008.php" gallery. This duplication is useful for my site visitors - User A may want to see goldfinch photos, whereas User B wants to see photos from New Mexico - but I am concerned about the SEO implications.
The typical suggestions to deal with duplicate content, such as 301 redirects and canonical tags, probably won't work in this case, because the page content is substantially different (ranging from ~1% to ~90% duplication, depending on the specific example chosen).
The obvious solution to me would be to edit robots.txt to only allow search engines to crawl one type of gallery - for instance, if they crawled only the galleries organized by species(e.g. goldfinch.php), all the photos on my site would be found exactly once. However, the Google content guidelines recommend against blocking crawler access to duplicate information.
Should I go ahead and use robots.txt anyway? Or is there a better solution?