Service to resize images uploaded to a WordPress site

According to the comments described in the question, I understood the problem and I think an interesting solution is to use ImageMagick, because of that I created this answer.

There is an ImageMagick port for Windows and can be downloaded here:

ImageMagick for Windows

Some of ImageMagick's advantages over any Web service are:

The program should be used by command line, see some examples below:

mogrify -resize 1600x1200 *.jpg

The above example resizes all files in the current folder to the resolution of 1600x1200. Note that the files after being processed will have the same name as the original (the files will be lost). Therefore, ensure that the command will not run on the original files.

mogrify -path imgs/ -resize 800x600 *.jpg

The command above will reduce the files of the current folder to 800x600 resolution, however, the processed files will be saved in the imgs folder (which, in the case above, must be inside the current folder). Thus, there is no risk that the original files will be modified.

There are several other options on the command line and this is one of the great advantages of ImageMagick.

Some examples of using ImageMagick More Examples

Two good online tools that do this are Quick Thumbnail and ResizeImageOnline .

A plugin is pretty easy :

<?php
/**
 * Plugin Name: (SOPT) Substituir Imagens Originais
 * Description: Substitui imagens originais (full size) pelo tamanho "grande" na hora do upload. 
   Ajuda a economizar espaço em disco, já que uma foto de 3240x4320 (5MB) pode se converter
   em uma de 768x1024 (108KB - exemplo depende do ajuste em /wp-admin/options-media.php e da qualidade jpeg). 
 * Author: brasofilo
 * Plugin URI: https://wordpress.stackexchange.com/a/54059/12615
 */

add_filter( 'wp_generate_attachment_metadata','replace_uploaded_image_wpse_48882' );
add_filter( 'jpeg_quality', 'qualidade_jpeg_sopt_19538' );

/**
 * Replace original by largest size on upload
 * 
 * @author brasofilo
 * @wp_hook wp_generate_attachment_metadata
 * 
 * @param object Image information
 * @return object
 */
function replace_uploaded_image_wpse_48882( $image_data ) 
{
    // if there is no large image : return
    if ( !isset( $image_data['sizes']['large'] ) ) 
        return $image_data;

    // paths to the uploaded image and the large image
    $upload_dir              = wp_upload_dir();
    $uploaded_image_location = $upload_dir['basedir'] . '/' . $image_data['file'];
    $large_image_location    = $upload_dir['path'] . '/' . $image_data['sizes']['large']['file'];

    // delete the uploaded image
    unlink( $uploaded_image_location );

    // rename the large image
    rename( $large_image_location, $uploaded_image_location );

    // update image metadata and return them
    $image_data['width']  = $image_data['sizes']['large']['width'];
    $image_data['height'] = $image_data['sizes']['large']['height'];
    unset($image_data['sizes']['large']);

    return $image_data;
}

/**
 * Qualidade: de 0 a 100
 */
function qualidade_jpeg_sopt_19538() 
{
    return 75;
}

You can also set JPEG quality advanced and use a custom size:

add_image_size( 'new-large', 1600, 1200 ); /* definido em functions.php ou num plugin */

• changing all occurrences of $image_data['sizes']['large'] by $image_data['sizes']['new-large'] .