figure/figcaption for images

add_filter( 'img_caption_shortcode', 'tumble_cleaner_caption', 10, 3 );

function tumble_cleaner_caption( $output, $attr, $content ) {

    /* We're not worried abut captions in feeds, so just return the output here. */
    if ( is_feed() )
        return $output;

    /* Set up the default arguments. */
    $defaults = array(
        'id' => '',
        'align' => 'alignnone',
        'width' => '',
        'caption' => ''
    );

    /* Merge the defaults with user input. */
    $attr = shortcode_atts( $defaults, $attr );

    /* If the width is less than 1 or there is no caption, return the content wrapped between the [caption]< tags. */
    if ( 1 > $attr['width'] || empty( $attr['caption'] ) )
        return $content;

    /* Set up the attributes for the caption <div>. */
    $attributes .= ' class="figure ' . esc_attr( $attr['align'] ) . '" style="width:'. esc_attr( $attr['width'] ) . 'px"';

    /* Open the caption <div>. */
    $output = '<figure' . $attributes .'>';

    /* Allow shortcodes for the content the caption was created for. */
    $output .= do_shortcode( $content );

    /* Append the caption text. */
    $output .= '<figcaption>' . $attr['caption'] . '</figcaption>';

    /* Close the caption </div>. */
    $output .= '</figure>';

    /* Return the formatted, clean caption. */
    return $output;
}

// Clean the output of attributes of images in editor. Courtesy of SitePoint. http://www.sitepoint.com/wordpress-change-img-tag-html/
function image_tag_class($class, $id, $align, $size) {
    $align = 'align' . esc_attr($align);
    return $align;
}

add_filter('get_image_tag_class', 'image_tag_class', 0, 4);

function image_tag($html, $id, $alt, $title) {
    return preg_replace(array(
            '/\s+width="\d+"/i',
            '/\s+height="\d+"/i',
            '/alt=""/i'
        ),
        array(
            '',
            '',
            '',
            'alt="' . $title . '"'
        ),
        $html);
}
add_filter('get_image_tag', 'image_tag', 0, 4);