Add thew following code just before the tag
<?php if (Mage::registry('current_product')) : ?>
<meta property="og:image" content="<?php echo Mage::helper('catalog/image')->init(Mage::registry('current_product'), 'small_image')->resize(100,100);?>" />
<meta property="og:title" content="<?php echo Mage::registry('current_product')->getName();?>" />
<?php endif;?>