how to set featured image in non-wordpress – SEO

pasting wordpress url in fb status bring a featured image+some text
while when I put mine (core php site) url in fb status, it shows only text but picking no image while I have more than 10 images at that page
I googled a lot but almost all posts are wordpress related while I couldn’t get how to make an image featured-image for a page on php/html (non-wordpress).
is there some html tag or attribute or some other method?