How can I set og:image

[pxjk]

Hi,

I'm trying to set the og:image for a client's site that pulls the first image used, instead of the logo.

I've tried adding og:image to the _header.php file in /public_html/themes/basis/views/layouts, however, Facebook only reads the first 50kb of data and therefore they're not picking it up.

Please can you advise which file I should be adding it to (or if there's a setting I'm missing in the admin dashboard) that will allow me to achieve the above?

Thanks,

Joe