Change Image Alt Attribute to Post Title / Post Category

/* Register callback function for post_thumbnail_html filter hook */
add_filter( 'the_content', 'post_image_alt_change', 10, 5 );

/* Function which will replace alt atribute to post title */
function post_image_alt_change( $html, $post_id, $post_thumbnail_id, $size, $attr ) {

    $post_title = get_the_title();
    $postcategories = get_the_category();
        $post_category='';
        if ($postcategories) {
          foreach($postcategories as $category) {
            $post_category .= $category->name .' ';
          }
        }
    $post_alt = $post_title . ' ' . $post_category;
    $html = preg_replace( '/(alt=")(.*?)(")/i', '$1'.esc_attr( $post_alt ).'$3', $html );
    return $html;
}