The move-scores of chess games that have been played are absolutely Public Domain.
No copyright.
Textual notes (ie: analysis by some speciific player) should always be credited... sometimes with a single word.
Eg: "This line is beautifully refuted by 14. Bh6!! (Fischer)".
That’s correct. Except for one nuance.
It should be: “This line is beautifully refuted by 14.Bh6!!” (Fischer). The reference is not part of the quotation, but it is part of the sentence.
Anyone can post a position from a game, but if the image and text exactly matches another’s post, you should credit the source.
Did Chess Skills steal this post from Rohan Dhore?

The move-scores of chess games that have been played are absolutely Public Domain.
No copyright.
Textual notes (ie: analysis by some speciific player) should always be credited... sometimes with a single word.
Eg: "This line is beautifully refuted by 14. Bh6!! (Fischer)".