Adding image tag into index.php?

Greetings,

I am using sporter theme for a long time. Problem I have with it is when sharing any website page (except pages with articles) on facebook or other social networks, it share just Page Title with Description...There is no image defined to be shared (logo of website or something)..

So I think there is missing image tag into index.php head, so please can you tell me is it the right way to correct it, and how to do that exactly..? Where is main index.php?

Or, if I am wrong, please give me instructions how to do that...Thanks!

Mladen

Hi,
templates/gk_sporter/layouts/default.php
that's all I can say.