SEO Duplicate Content: There is a myth among SEO professionals called Google penalty for duplicate content. Many SEO professionals say that Google penalizes sites that have duplicate content. This information does not follow! There is duplicate content within a site, duplicate content on the network, such as news, for example, and copying content, ie, theft of content.
Duplicate content within the site: 
Most of the time you provide the same content on different URLs, as is the case of an e-commerce, for example, that uses session IDs.
For example:
- http://www.example.com
- https://www.example.com
- http://www.example.com/index.htm
- https://www.example.com/index.htm
- http://example.com
- https://example.com
- http://example.com/index.htm
- https://example.com/index.htm
- https://example.com/index.htm
To resolve this problem you can choose the URL of your own, that you really want to appear in the search and do a 301 redirect to other URLs so that all just point to the URL you have chosen. If you can not do this redirection use the rel = “canonical” for the search engines to better understand your site and its distinct URLs.
The goal is to make the search engines know that these pages have the same contents and index only one version to display them in the search results.
Can also occur in some cases, you have two pages with the same content and one of them being a version just for printing. In this case you should put a meta noindex tag in the print version. If you do not tell Google which page to be indexed will choose one of the two and he may choose exactly the print version.
Duplicate content on the network:
You can, for example, republish the post in your blog, provided you cite the source and the author has a link to the original post. This is perfectly correct, and Google will not punish you for it.
Google knows when your content is duplicated as in the examples above and will not be any punishment in such cases.
Duplicate content (theft of content):
You develop a site and someone unscrupulous uncreative copy your HTML, your pictures, finally, the entire contents of your site and will publish the contents stolen. If you discover, report it to Google and prove that this content is yours, he will be punished. But in this case since it is not duplicate content, but theft of content.
Obviously we are not talking about manipulation of the classification results using techniques of Black Hat SEO. In this case not only duplicate content, stolen and otherwise attempt to manipulate the search engines, especially Google, your site will be banned from the index!
The duplicate content problem has finally been resolved with Google’s new canonical element. Web developers can indicate their preferred page URL using a new
tag in the HTML .
For example:
<link rel=”canonical” href=http://www.example.com/ />
inside the <head> section of the duplicate content URLs:
Note:
- The canonical URL must be on the same domain, although sub-domains such as www.mysite.com and products.mysite.com are permitted.
- Relative path names are handled and Google will resolve URLs to any path set by the page’s link.
- The preferred URL does not need to contain an exact replica of the original page content. Google will permit slight differences, such as the order of a list of products. However, it is certainly advisable to avoid that situation where possible.
- Google will follow canonical chains, but recommend that a single valid URL is specified for the best results.
Thanks for the post. I stumbled upon this article on twitter.
Do keep up with the posts.
Paul
Cheer Paul.