Copyright comes into being from the date of completion of the work, and whether it is protected by law through copyright registration (that is, registration as you said). Do you know how many photos photographers all over the world take every day? Do you know how many pictures are the copyright of the big picture sales company? Everyone should register the copyright, and the people in the copyright bureau should commit suicide.
No one else is a fool. If the obligee finds out that your trademark is modified from the obligee's picture, the obligee will claim your rights. You can deny that you created the material yourself. It depends on what evidence you can submit to prove that it is original, and it depends on how the judge decides.
The first floor is wrong. If it can be registered, it is not infringement. Are there still few lawsuits for registered trademarks? What the court has decided or changed can guarantee that you will not be sued for infringement.