Make at least one photo that shows that you created it.
Write your @username on a piece of paper, put it on the same table with food and make a photo with it. That's it.
If your images was posted on other sites, just put a link and write that is your other site or whatever.
So, you do not have to explain how those images got there before you posted it on Steemit.
For example: every time we go home, we don't need to knock on the door. Why? Because this is my own home, the picture is the same, and the pictures I took are my own. If you follow your opinion, is it true that all authors are required to take a selfie certificate when they take pictures? Otherwise is it a violation? That's ridiculous! Not happy, wait until you are happy, then share it.
You even behave like a bad actor. Instead of providing proof you give cheap talk.