你可以挂上过滤器img_caption_shortcode 并替换整个标题图像。这里，我复制了WP4中的caption shortcode函数。5，如果主题声明支持HTML5（使用figcaption），并将非HTML5版本修改为使用h2，则保留使用的版本。

function wpse_233354_img_caption_shortcode( $empty, $attr, $content = null ) {
    // New-style shortcode with the caption inside the shortcode with the link and image tags.
    if ( ! isset( $attr[\'caption\'] ) ) {
        if ( preg_match( \'#((?:<a [^>]+>\\s*)?<img [^>]+>(?:\\s*</a>)?)(.*)#is\', $content, $matches ) ) {
            $content = $matches[1];
            $attr[\'caption\'] = trim( $matches[2] );
        }
    } elseif ( strpos( $attr[\'caption\'], \'<\' ) !== false ) {
        $attr[\'caption\'] = wp_kses( $attr[\'caption\'], \'post\' );
    }

    $atts = shortcode_atts( array(
        \'id\'      => \'\',
        \'align\'   => \'alignnone\',
        \'width\'   => \'\',
        \'caption\' => \'\',
        \'class\'   => \'\',
    ), $attr, \'caption\' );

    $atts[\'width\'] = (int) $atts[\'width\'];
    if ( $atts[\'width\'] < 1 || empty( $atts[\'caption\'] ) )
        return $content;

    if ( ! empty( $atts[\'id\'] ) )
        $atts[\'id\'] = \'id="\' . esc_attr( sanitize_html_class( $atts[\'id\'] ) ) . \'" \';

    $class = trim( \'wp-caption \' . $atts[\'align\'] . \' \' . $atts[\'class\'] );

    $html5 = current_theme_supports( \'html5\', \'caption\' );
    // HTML5 captions never added the extra 10px to the image width
    $width = $html5 ? $atts[\'width\'] : ( 10 + $atts[\'width\'] );

    /**
     * Filter the width of an image\'s caption.
     *
     * By default, the caption is 10 pixels greater than the width of the image,
     * to prevent post content from running up against a floated image.
     *
     * @since 3.7.0
     *
     * @see img_caption_shortcode()
     *
     * @param int    $width    Width of the caption in pixels. To remove this inline style,
     *                         return zero.
     * @param array  $atts     Attributes of the caption shortcode.
     * @param string $content  The image element, possibly wrapped in a hyperlink.
     */
    $caption_width = apply_filters( \'img_caption_shortcode_width\', $width, $atts, $content );

    $style = \'\';
    if ( $caption_width )
        $style = \'style="width: \' . (int) $caption_width . \'px" \';

    $html = \'\';
    if ( $html5 ) {
        $html = \'<figure \' . $atts[\'id\'] . $style . \'class="\' . esc_attr( $class ) . \'">\'
        . do_shortcode( $content ) . \'<figcaption class="wp-caption-text">\' . $atts[\'caption\'] . \'</figcaption></figure>\';
    } else {
        $html = \'<div \' . $atts[\'id\'] . $style . \'class="\' . esc_attr( $class ) . \'">\'
        . do_shortcode( $content ) . \'<h2 class="wp-caption-text">\' . $atts[\'caption\'] . \'</h2></div>\';
    }

    return $html;
}

add_filter( \'img_caption_shortcode\', \'wpse_233354_img_caption_shortcode\', 10, 3 );