ASFAIK even CGTextures don’t want you using their images in Blender. Because Blender offers no protection. Anyone can just copy whatever they want from a Blend file. Unlike Unity and Unreal.
But you could use a copy protected image as reference. Say you wanted a monster.
So you search for images and find a monster you like. But it’s copy protected.
But you DL the image anyway and open in Blender.
You model in Blender a monster from the image and change it a little. Use the images texture for the monster skin, eyes etc.
Then bake that to another image, or even take a screenshot of the monster from several angles. open that/those image in PS or Gimp, to make your texture map, and change it up so that no one would even recognize the original image, or the monster. UV map using the new texture map.
Remove the copywrited image from the Blend file. (In UV image shift + click the X on the image, restart the Blend file)
I’m no lawyer, so I don’t know if that’s legal.
Not sure about the morality issue.
I did that a few times.