Indexhibit Support

Hi. I found this video youtube.com/… on how to create a facebook preview thumbnail for my website. Is the video correct?

As the video says, I added

to my index.php. (Is the code right? Should I add this in Admin>Assets>index.php or go to FileZilla and change my index.php file there? Is there a difference?) And I left this image in my root directory. Nothing happened.

the code i added was

link rel='image_src' href='marcqimengzhao.com/index.php/photographs/new-london-italy/…'

omg am i being dumb again? Does the Face Meta plugin do this easily?