You can use the timthumb for resize your images as you want.
if ( has_post_thumbnail() ) {
// get the src of the large size featured image
$src = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'large' );
$thumbnailSrc = $src[0];
// output image resized with timthumb
?>
<a href="https://wordpress.stackexchange.com/questions/97632/<?php echo get_post_meta($postid,"post_link', true) ?>" target="_blank">
<img src="<?php bloginfo('template_directory'); ?>/js/timthumb.php?src=<?php echo $thumbnailSrc; ?>&h=240&w=245" alt="">
</a>
<?php } ?>
And download that file timthumb
Hopefully your problem solve.