Yes sadly there's no way to protec against thatt. But in the internet artistic community, stealing is frowned upon and the thief will be taken care of, as happened in your case. Justice is served.
Even thiugh you don't create a file in Photoshop' you can open it iin Photoshop and put your copyright and other info in the file as metadata. Even if they take your name off they will be unaware that is there.
Just go to File / File Info and take it from there.
Don't operate in fear.you never know what opportunity you may lose because your art wasn't seen by not posting out of fear. A copyright does not protect your art from getting stolen either, just gives you a stronger case to bring to court.
Once the art is out there someone can take it.