You have done the right thing. So proud of you for that! It's in your best interests and also Steemit's. In the long run you will see it has been worth it.
There are specific ways you can use the actual free images, and you need to learn that you can never ever misrepresent them by seeming to claim they you created them.
The problem is, you may pick up an image like you did because others have been taking it, and you don't know the source. You honestly think it is free. Others post it making it look like it is free. Often the_"free"_ sites also have stolen images. I've had to have a few of mine removed from there in the past!
The best thing by far to do is to use your own work. In #colorchallenge, those are the rules anyway. It's to showcase your own work.
But if you are going to use photos from the web for an editorial blog (not just to get attention), research the photograph all the way back to the photographer or agency before assuming it is free because someone else used it as free.
All the best!