help! client's Illustrator doc showing faint black ghost outline

I am trying to help with an .ai document I did not create. It has multiple layers and when they save as PDF, a faint black outline appears behind one of the images but an inch below it--just the outline of that image shape, not the shape itself. Their concern is whether that outline, which is not intentional, will appear when printing. Obviously the best thing would be to figure how to remove/prevent it, before sending to printer.

My question is: how can I try to fix this issue? and second, a general question that I need help on, is that since this is a file with lots of linked images, do I need to update every single link for viewing on my own computer before I can even try to recreate the ghost outline effect? I am a novice as you can tell, just cracking into Illustrator, and the complexities are many...

thanks!!