You do not have to technically attribute the author for public domain works but it's still the decent and professional thing to do. As for when you do need to attribute an author, I happen to have experience using creative commons photos. What I do is click on "use this file on the web" and a pop up displays some options. I then copy the "attribution" line and paste that into the "caption" for the image I'm using on the post.
Then I copy the url's and use this code to make hyperlinks:
<a href="
url">
link text</a>
I would paste the long URL in between the quotations and the subsequent text, which is usually the licence type.
For example, to use this painting attribution:
By Schiwago (Own work (selbst fotografiert)) [GFDL (
http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (
http://creativecommons.org/licenses/by-sa/3.0/) or CC BY 2.5 (
http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons
I would change it to this in the Word Press media caption box:
By Schiwago (Own work (selbst fotografiert)) [<a href="http://www.gnu.org/copyleft/fdl.html" > GFDL</a>, <a href="http://creativecommons.org/licenses/by-sa/3.0/" >CC-BY-SA-3.0 </a> or <a href= "http://creativecommons.org/licenses/by/2.5">CC BY 2.5</a>], via Wikimedia Commons
Which winds up looking like this on your front end blog post:
By Schiwago (Own work (selbst fotografiert)) [
GFDL,
CC-BY-SA-3.0 or
CC BY 2.5], via Wikimedia Commons
Normally there's not that many parentheses where "own work" is, so typically it will look better. Attribution text varies from image to image though. Hope this helps.