Reduces size of images in posts using bfi_thumb

content_img_filter.php

<?php
require_once('BFI_Thumb.php');

add_filter( 'the_content', 'itc_the_content_img_filter', 999 );
/**
* Reduces size of images in posts using bfi_thumb
*
*/
function itc_the_content_img_filter( $content ) {
 /* Add here the width you prefer (max width of your posts) */ 
	$max_width = 600;

	preg_match_all("{<img.*src=\"(.*?)\".*width=\"([0-9]*)\"\s*height=\"([0-9]*)\".*/>}",$content, $images);
	
	foreach($images[1] as $key => $image){
		$new = $images[0][$key];
		if($images[2][$key] > $max_width){
			$params = array('width' => $max_width);
			$new = str_replace('src="'.$image.'"', 'src="'.bfi_thumb( $image, $params ).'"', $new);
			$new = str_replace('width="'.$images[2][$key].'"', 'width="'.$max_width.'"', $new);
			$new_height = round($images[3][$key]*$max_width/$images[2][$key]);
			$new = str_replace('height="'.$images[3][$key].'"', 'height="'.$new_height.'"', $new);
		} else {
			$params = array('width' => $images[2][$key]);
			$new = str_replace('src="'.$image.'"', 'src="'.bfi_thumb( $image, $params ).'"', $new);
		}
		$content = str_replace($images[0][$key], $new ,$content);
	}
	return $content;
}