Ok, 1st of all, this is a javacript question, which is why we are not answering. Try posting this in the javascript forum. I can see how you would think it would go here, but this is for the graphical side of multimedia, not the code used to play it.
The second question is a CSS question. I have an example of that
here, which you can check out. How I did this in short was by placing the overlay image in a div below the media player, applying relative positioning, and then using a negative "top" value to bring it up and over the media player.