To note, these are portraits compiled of those being actively used by characters in this PW. As such, and because NWN will encounter problems during character creation if you have too many Portrait files in your Portrait directory, 99% of these are in the Override section, meaning you can see them in game, but not on character creation.

If you can't get it to work, moving the files from your Overrides folder to your My Documents/Neverwinter Nights/Portraits folder instead should also work. It's the only way I got it to function for me.

Same thing - if it's not working for you, you can go into your steam workshop files and copy the files manually to your My Documents/Neverwinter Nights/ folder instead.