I had added streak marks to indicate a rapid movement of the ball and stretched out the puppy's body to give the impression he was moving toward the viewer.
A charge of plagiarism is a very serious accusation and should only be made on the basis of strong evidence. It is currently very difficult to prove or disprove a charge of plagiarism in the MOOC peer assessment setting. As a result, I am not expecting you to police your classmates’ work for plagiarism. You should evaluate the work of your classmates on the merits of what they have submitted. You should only mark them down if you are absolutely 100% confident that their submission constitutes an act of egregious plagiarism. I am not in a position to evaluate whether or not a submission actually constitutes plagiarism, and I will not be able to entertain appeals or to alter any grades that have been assigned through the peer evaluation system.
In a MOOC, your teacher is not there to defend you. The Coursera professor is too busy; there are too many students. You have no recourse on Coursera.
Coursera announced there are now 2.7 million people enrolled in their courses. Would you trust your college grade to be crowd-sourced by a random sampling of millions of people around the world?