As more and more marketers and others curate content in their content marketing efforts, they need to be aware of the legalities of using content that isn't theirs.
In some situations, if you use content without the right sort of permission, you may find yourself being sued by the content creator.
For example, uploading someone else's photo to your site without permission is infringement. That photo credit that you gave them doesn't mean anything; however, a link to the photo is legal (if the content itself is legal).
Quoting people's content is also a popular practice among marketers. But be careful to not quote too much of it, lest you end up plagiarizing rather than paying it homage.