ejos

I solve the problem by changing the function build_metadata() on file plugins/amp/class-amp-post.php to:

private function build_metadata() {

                $data = array(
                        '@context' => 'http://schema.org',
                        '@type' => 'BlogPosting', // TODO: change this for pages
                        'mainEntityOfPage' => get_permalink( $this->ID ),
                        'headline' => get_the_title( $this->ID ),
                        'datePublished' => get_the_date( 'c', $this->ID ),
                        'dateModified'=> get_post_modified_time( 'c','' , $this->ID ),
                        'author' => array(
                                '@type' => 'Person',
                                'name' => $this->author->display_name,
                        ),
                        'image' => array(
                                        '@type' => 'ImageObject',
                                        'url' => get_the_post_thumbnail_url($this->ID),
                                        'width' => '696',
                                        'height' => '580',

                        ),
                        'publisher' => array(
                                '@type' => 'Organization',
                                'name' => get_bloginfo( 'name' ),
                                'logo' => array(
                                        '@type' => 'ImageObject',
                                        'url' => 'http://url_to_my_logo.jpg',
                                        'width' => '187',
                                        'height' => '143',
                                ),
                        ),
                );

                return $data;
        }

Width and height values are my custom values you should change them with your own values.

hope it helps