1.By using the default featured image plugin
2.By manually add the necessary code in your theme’s file that displays the posts thumbnail such as index.php, single.php, home.php etc..)
This is the code you need to add
<?php if ( has_post_thumbnail() ) {
the_post_thumbnail();
} else { ?>
<img src="<?php bloginfo('yout_template_directory'); ?>/images/default-yourimage.jpg" alt="<?php your title(); ?>" />
<?php } ?>
Edited by OneDes, 19 November 2013 - 01:37 AM.