resize.php

<?php
function post_image($post, $targetwidth = 100, $targetheight = 100, $resize = true){
	$key="post-image";
	$post_image = get_post_meta($post->ID, $key, true);	
	if ($post_image != null) {
		//get image size
		$width = get_post_meta($post->ID, "post-image-width", true);
		$height = get_post_meta($post->ID, "post-image-height", true);
		if ($width == null || $height == null){
			//only calculates the size for the first time.
			list($width, $height, $type, $attr) = getimagesize($post_image);
			if(!update_post_meta($post->ID, "post-image-width", $width))
				add_post_meta($post->ID, "post-image-width", $width, true);
			if(!update_post_meta($post->ID, "post-image-height", $height))
				add_post_meta($post->ID, "post-image-height", $height, true);				
		}
		if (!$resize){
			printf ('<img src="%s" height=%d />', $post_image, $targetheight);
			return;		
		}
		else if (($width/$height) < ($targetwidth/$targetheight)){
			printf ('<img src="%s" width=%d />', $post_image, $targetwidth);		
		}else{
			printf ('<img src="%s" height=%d />', $post_image, $targetheight);
		}
	}
}
?>