WordPress recreate thumbnails

Script to regenerate or adjust all thumbnail sizes from original source images within a WordPress blog. Useful when sizes have changed due to a switch/update of theme or the modification of add_image_size() setup.

Whilst there are a number of regenerate image utilities already available, most if not all are implemented as WordPress plugins - thus their processing happens within a HTTP request slowing things down, timing out and/or taking a large amount of time to complete due to the need of incremental processing.

Script should be called from the PHP CLI and gets the job done as fast as your CPU allows - it was written for a WordPress blog containing well over 4GB of images where a plugin style utility wasn't really going to cut it. Having said that, it is rather manual and can be destructive - a reliable and tested backup and some decent knowledge of the WordPress image sizes system is strongly advisable.

In addition a second find orphan images script can be executed after successful image regeneration, which seeks out images present under /wp-content/uploads/[YEAR]/[MONTH] that are no longer referenced and moves them outside of the /wp-content/uploads/ path.

• Requires
• Rebuild thumbnails
  • Usage
• Find orphan images
  • Usage

Requires

• PHP 5.5.
• GD for thumbnail image creation.
• MySQLi with MySQL native driver.

Rebuild thumbnails

The wordpressrebuildthumbnails.php script performs the following tasks:

• Loads all wp_posts of type attachment.
• Extracts the origin image filename from the guid field, ensures image actually exists on disk and corrects post_mime_type for the image if required.
• Ensures attachment has both _wp_attached_file and _wp_attachment_metadata rows in the wp_postmeta table, creates if they do not exist.
• Validates serialized PHP data in _wp_attachment_metadata for origin image size and path, corrects if required.
• Works over existing thumbnail sizes for the image attachment, validates file existence, image dimensions and if the size is actually required - drops if required.
• Creates image sizes for new additions and/or sizes dropped in the previous step due to invalid data. Image resize dimensions are based on the same algorithms as used by WordPress (wp_constrain_dimensions() and image_resize_dimensions() found in /wp-includes/media.php) and like WordPress images that would be generated larger than the origin image will be skipped. Additionally recreated images will have a sharpen applied using the imageconvolution() GD function.
• Remove any orphan image sizes (e.g. my_base_image_name-UNUSED_WIDTH-UNUSED_HEIGHT.jpg) that are no longer required for the attachment from disk.
• Finally updates database _wp_attachment_metadata for the associated wp_postmeta row.

The script will only modify/resize images when required - if previous images meet the defined size requirements they will not be regenerated. This means the script can be re-run to validate all database data lines up with disk image files.

Usage

Configure the constants at the top of wordpressrebuildthumbnails.php to suit. Details of each setting are as follows:

DB_SERVER	Hostname/socket of the MySQL database. Typically would be localhost.
DB_USER	MySQL database login user.
DB_PASSWORD	MySQL database login password.
DB_DATABASE	MySQL database name containing WordPress blog tables.
JPEG_IMAGE_QUALITY	Save quality for JPEG image types between 0-100.
PUBLIC_SITE_UPLOADS_URL	Full public URL path to the /wp-content/uploads/ folder, including trailing forward slash. This is used to construct the regular expression for extracting internal blog post image references.
PATH_TO_UPLOADS	Full/relative (to script) path containing all WordPress blog images, with trailing slash.
LOG_FILE_PATH	Log file name used to output any unrepairable errors during processing.

Next, add your desired image sizes to the bottom of wordpressrebuildthumbnails.php as an array passed into the WordPressRebuildThumbnails() constructor. Each array provides the width, height and crop settings per size - matching the add_image_size() WordPress method.

It would be wise to at least provide the WordPress default sizes of thumbnail, medium and large.

Example:

new WordPressRebuildThumbnails([
	'thumbnail' => [300,275,true],
	'medium' => [610,610],
	'large' => [960,960]
]);

Now execute the script from the destination WordPress blog server/location via CLI and let it do its work.

$ php wordpressrebuildthumbnails.php

Find orphan images

After you are happy with the thumbnail regeneration process, the wordpressfindorphanimages.php script can be used to determine the following:

• Any images located under /wp-content/uploads/[YEAR]/[MONTH] which are never referenced within any _wp_attachment_metadata database records.
• Images referenced in _wp_attachment_metadata which are missing from /wp-content/uploads/ on disk.

Usage

Similar configuration to the resize script above, with the following additional settings:

LOG_FILE_UNUSED_PATH	File to save a listing of all unused/unreferenced images.
LOG_FILE_UNUSED_BASH_PATH	Bash script to assist in the moving of all unused/unreferenced images from /wp-content/uploads/ (see below for details).
LOG_FILE_MISSING_PATH	File to save a listing of all images defined in attachment database rows that could not be located on disk.

Now execute the script from the destination WordPress blog server/location via CLI and let it do its work.

$ php wordpressfindorphanimages.php

An example of the generated LOG_FILE_UNUSED_BASH_PATH bash script is as follows, allowing for an easy moving out of unused images:

#!/bin/bash
SOURCE_IMAGE_DIR=/path/to/wp-uploads/
DEST_UNUSED_IMAGE_DIR=/tmp/wp-unused/update/to/suit/

mkdir -p ${DEST_UNUSED_IMAGE_DIR}2014/02
mv ${SOURCE_IMAGE_DIR}first-image.jpg ${DEST_UNUSED_IMAGE_DIR}2014/02
mv ${SOURCE_IMAGE_DIR}second-image.jpg ${DEST_UNUSED_IMAGE_DIR}2014/02
mv ${SOURCE_IMAGE_DIR}third-image.jpg ${DEST_UNUSED_IMAGE_DIR}2014/02
mkdir -p ${DEST_UNUSED_IMAGE_DIR}2014/03
mv ${SOURCE_IMAGE_DIR}fourth-image.jpg ${DEST_UNUSED_IMAGE_DIR}2014/03
mv ${SOURCE_IMAGE_DIR}fifth-image.jpg ${DEST_UNUSED_IMAGE_DIR}2014/03
mv ${SOURCE_IMAGE_DIR}sixth-image.jpg ${DEST_UNUSED_IMAGE_DIR}2014/03

DEST_UNUSED_IMAGE_DIR should be updated to suit before executing the bash script.