Hi Cedriklizotte,
As per your queries, you have recently discovered about the rel="canonical" tag so let's try to understand this first. As you have mentioned that some of the pages redirect to the "original content". So its better to put the rel="canonical" tag to the original link because that'll be the preferred URL when it comes to tell the search engines about which page to consider as the "original content". So this code would look like:
And put this code in the section of the page.
Now, let's try to answer your questions one by one:
Question: If, on my blog, I have a blog post that's the original. And another website has the same content, used with authorization. If I want to tell search engines that the original content is on MY blog, what can I do? Is the only solution to ask the owner of the other blog to add a rel=canonical in the header of the specific post?
Answer: In this scenario, as you suggested its better to ask the owner of the other blog to add a rel=canonical with the link to your blog in the section of the specific post.
Question: If, on my blog, I have a blog post that's NOT the original. Do I simply add rel=canonical to the header, then add a link to the original in the body?
Answer: You should mark up the page with the rel=canonical tag in the section in the format that I have mentioned.
If the body has a CTA (Call To Action) button that takes to the original post then put the link there and no need to put rel=canonical tag there because you have already put the rel=canonical tag in that page with the preferred URL or original link.
Question: If, on my blog, I have THE FIRST 300 WORDS of a blog post, then add a link saying "to read the whole article, click here" with a link pointing to the original, do I need to have a rel=canonical tag somewhere? Does it HAVE to be in the header?
Answer: Yes, better to put the rel=canonical in the header.
Question: Can rel=canonical be used in the
_[Answer: Yes, rel=canonical is always used in the <href=>element format of a link in order to tell search engines that the original of content is actually on the other blog.</href=>
Question: What penalties are included with having duplicate content of my work everywhere on the web? I've been trying to find specifics, but can't.
Answer: Just check this link: https://webmasters.googleblog.com/2008/09/demystifying-duplicate-content-penalty.html from Google Webmasters blog about the duplicate content penalties and you'll get a fair idea about the specifics.
I hope this would help.
Regards,
Amit Rathi](code)_
