Official or not, if they are not yours or from the site that doesn't protect its content or doesn't require attribution, source link should be provided or it's considered as plagiarism.

This is just a friendly advice, as you apparently put lots of efforts in the article creation and its uniqueness, from my point of view, it would be a pity that you fall on that one and risk to be downvoted or even blacklisted.
As I said, just a friendly advice because of images, illustrations, etc. also has its authors who hold some copyrights the same as the authors of textual content do too.