Question: How can you get an image alt attribute in WordPress using the URL?

To retrieve the alt attribute of an image in WordPress using its URL, you need to leverage WordPress's built-in functions. Here is a sample PHP function that accomplishes this:

function get_image_alt_by_url( $image_url ) {
    global $wpdb;
    
    // Get the image ID from the database
    $attachment_id = $wpdb->get_var( $wpdb->prepare( "SELECT ID FROM $wpdb->posts WHERE guid='%s';", $image_url ) );

    // Get the alt text from the image metadata
    $alt_text = get_post_meta( $attachment_id, '_wp_attachment_image_alt', true );
    
    return $alt_text;
}

In the above code:

1. We're using $wpdb, WordPress's class for interacting with the database.
2. We find the ID of the image (a.k.a., the attachment post) whose guid (Globally Unique Identifier) matches the provided URL. The guid field in the WordPress database typically stores the URL of the media file.
3. Once we have the image ID, we use the get_post_meta() function with _wp_attachment_image_alt as the meta key to fetch the alt text.

This function will return the alt text corresponding to the given image URL. If no alt text is found, it returns an empty string.

Please note that the guid field in the WordPress database is not always guaranteed to hold the media URL and it should not be used to find the media URL of an attachment. But it's generally reliable for sites that don't change their domain or move their uploaded files after they've been added to the database.