Icon Button needs to point to another field

I am creating a form where the end user has to upload an image. I am trying to customize it so that there is a masked PNG in front of the upload image form field so that when they upload an image instead of it being a square it will be masked out as a circle. 

So all I really need is a javascript that will make the "masked PNG" button point to the "Upload Image" form field so that the end user can upload their image.

Let me know if I need to provide anything.