Of course it's OK, but this way you pretend they are your photos. It would only be fair, even if the photos are CC0 licensed. Link tothe original author's portfolio page at Pexels or Pixabay or wherever. I also have photos on several CC0 sites and sometimes I even get paid by users and many times I get a "thank you" etc and this makes me happy, like all other authors and photographers out there.
Of course we are giving the photos away for free with CC0 license, but we are doing this with the intention to be noticed by others ... what you are doing is to go to Pixabay, look for a nice picture, copy it and add a few words to pretend you are what you are not.
And you may of course carry on doing what you are doing since CC0 is CC0...
So, to bring it to an end: Honesty and fairness are very important here.