get total number of images from media using xml-rpc

VERSION 1 will query all the images and give you a count by checking the size of the returned array. VERSION 2 is a much faster method introduced by birgire.

// VERSION 1

    $images = get_posts(array(
        'post_type'         => 'attachment',
        'post_status'       => 'any',
        'numberposts'       => -1,
        'fields'            => 'ids',
        'post_mime_type'    => 'image/jpeg,image/gif,image/jpg,image/png',
    ));

    echo count($images) . ' images total';

// VERSION 2

    $count = array_sum( (array) wp_count_attachments( 'image' ) );

    echo "{$count} images total";

---

ORIGINAL – For a full XML-RPC solution, create a custom method.

function xml_add_method( $methods ) {
    $methods['myNamespace.attachmentCount'] = 'get_attachment_count';
    return $methods;
}
add_filter( 'xmlrpc_methods', 'xml_add_method' );

function get_attachment_count( $args ) {
    // good to know it's here
    // global $wpdb; 

    // params passed in the call - not needed in this example
    $params = $args[3];

    // count the posts then return the total value
    $images = get_posts(array(
        'post_type'         => 'attachment',
        'post_status'       => 'any',
        'numberposts'       => -1,
        'fields'            => 'ids',
        'post_mime_type'    => 'image/jpeg,image/gif,image/jpg,image/png',
    ));

    // images total
    return count($images); 
}

Then do the RPC

global $current_user;

$user = $current_user->user_login;
$password = $user->data->user_pass;

include_once( ABSPATH . WPINC . '/class-IXR.php' );
include_once( ABSPATH . WPINC . '/class-wp-http-ixr-client.php' );
$xmlrpc_url = home_url('xmlrpc.php');
$client = new WP_HTTP_IXR_CLIENT( $xmlrpc_url );

// set this to true if you need help
// $client->debug = true;

$response = $client->query( 'myNamespace.attachmentCount', array(
    0,
    $user,
    $password,
    array(
        'post_type'         => 'attachment',
        'post_status'       => 'any',
    )
) );

if ( is_wp_error( $response ) ) {
    $error_message = $response->get_error_message();
    echo "Something went wrong: $error_message";
} else {
    echo 'Response:<pre>';        
    $count = $client->message->params[0]; // our return value is here
    print_r( $count . ' images total' );
    echo '</pre>';
}

---

UPDATE
Merging @birgire’s solution into this one.

---

add_filter('xmlrpc_methods', function ($methods) {
    $methods['myNamespace.getTotalImageCount'] = 'rpc_myNamespace_getTotalImageCount';
    return $methods;
});

function rpc_myNamespace_getTotalImageCount($args)
{
    return array_sum((array)wp_count_attachments('image'));
}

add_action('parse_request', function () {

    // PULL USER CREDS FROM CURRENT USER
    global $current_user;

    $user = $current_user->user_login;
    $password = $user->data->user_pass;

    include_once(ABSPATH . WPINC . '/class-IXR.php');
    include_once(ABSPATH . WPINC . '/class-wp-http-ixr-client.php');
    $xmlrpc_url = home_url('xmlrpc.php');
    $client = new WP_HTTP_IXR_CLIENT($xmlrpc_url);

    // CALL OUR CUSTOM METHOD
    $response = $client->query('myNamespace.getTotalImageCount', array(0, $user, $password));

    echo 'Response:<pre>';
    $count = $client->message->params[0];
    print_r("{$count} total images");
    echo '</pre>';

    wp_die('FIN');
});