Get an attachment ID given a URL

get-attachment-id-from-url.php

<?php

/**
 * Get an attachment ID given a URL.
 *
 * @param   string $url URL to check.
 *
 * @return  int Attachment ID on success, 0 on failure.
 */
function get_attachment_id( $url ) {

	$attachment_id = 0;

	$dir = wp_upload_dir();

	// Is URL in uploads directory?
	if ( false !== strpos( $url, $dir['baseurl'] . '/' ) ) {

		$file = basename( $url );

		$query_args = array(
			'post_type'   => 'attachment',
			'post_status' => 'inherit',
			'fields'      => 'ids',
			'meta_query'  => array(
				array(
					'value'   => $file,
					'compare' => 'LIKE',
					'key'     => '_wp_attachment_metadata',
				),
			),
		);

		$query = new WP_Query( $query_args );

		if ( $query->have_posts() ) {

			foreach ( $query->posts as $post_id ) {

				$meta = wp_get_attachment_metadata( $post_id );

				$original_file       = basename( $meta['file'] );
				$cropped_image_files = wp_list_pluck( $meta['sizes'], 'file' );

				if ( $original_file === $file || in_array( $file, $cropped_image_files ) ) {

					$attachment_id = $post_id;
					break;

				}
			}
		}
	}

	return $attachment_id;
}