Quickly convert all images in the given and sub-directories to JPGs.

convert.php

<?php
/**
 * Converts all images in this directory and all subdirectories into JPGs.
 * 
 * Example: php convert.php ~/Images
 * 
 * Takes a directory as its only parameter and traverses it recursively looking for images. Whenever an image is found,
 * this creates a copy of the image with the same name and the extension .jpg. Images with the extension .jpg will 
 * be overwritten.
 * 
 * Author: Dimitry Zolotaryov (dimitry@webit.ca)
 * Copyright: 2013 Dimitry Zolotaryov, MIT License
 */

if ( $argc < 2 ) die("Usage: convert.php [directory]");

$input_dir = $argv[1];
$full_dir  = realpath( $input_dir );

if ( is_dir( $full_dir ) && is_readable( $full_dir ) ) {
    print "Reading $full_dir for images\n";
    convert_dir( $full_dir, array( 'echo' => true ) );
} else {
    die( "$full_dir is not an accessible directory." );
}


/**
 * Converts all .gif and .tif files in a directory to jpg.
 *
 */
function convert_dir( $directory, $options = array() )
{
    $directory = rtrim( $directory, DIRECTORY_SEPARATOR );
    if ( !empty( $options['echo'] ) ) {
        print "Reading directory $directory\n";
    }

    if ( $handle = opendir( $directory ) ) {
        while ( false !== ( $entry = readdir( $handle ) ) ) {
            $full_entry = $directory . DIRECTORY_SEPARATOR . $entry;
            if ( is_dir( $full_entry ) && substr( $entry, 0, 1 ) != '.' ) {
                convert_dir( $full_entry, $options );
            } else if ( is_file( $full_entry ) ) {
                convert_file( $full_entry, $options );
            }
        }
        closedir( $handle );
    } else {
        if ( !empty( $options['echo'] ) ) {
            print "Could not read $directory\n";
        }
    }
}

/**
 * Converts the given .gif or .tif file to a .jpg of the same name.
 */
function convert_file( $file, $options = array() )
{
    if ( !is_file( $file ) ) {
        return;
    }

    if ( !getimagesize( $file ) ) {
        if ( !empty( $options['echo'] ) ) {
            print "Image $file is empty or not an image\n";
        }
        return;
    }

    $image = new Imagick( $file );

    $file_info = pathinfo( $file );
    $new_file = $file_info['dirname'] . DIRECTORY_SEPARATOR . $file_info['filename'] . '.jpg';

    if ( file_exists( $new_file ) ) {
        if ( !empty( $options['echo'] ) ) {
            print "JPG $new_file already exists\n";
        }
        return;
    }

    $image->setFormat( 'jpg' );

    if ( !empty( $options['echo'] ) ) {
        print "Writing $new_file\n";
    }

    if ( !$image->writeImage( $new_file ) ) {
        if ( !empty( $options['echo'] ) ) {
            print "Could not write image $new_file\n";
        }
    } else {
        return true;
    } 
}