It is true that, in academia, reproduction of any work by others, including images, graphs and music without attribution is regarded as plagiarism, but the working definition of plagiarism on this forum seems to be "taking credit for someone else's writing as your own," which is a valid and widely used definition in itself.
Your example shows why there is no danger of reproduction of most images being taken as an attempt to take credit for their creation, the fact that it is a third party creation is implicit in its being shared.
"Violating the private life" is not possible by linking to public domain material.
You could have chosen any of a million unattributed images posted on the forum, but you used that one. Why's that?