upload image only

I edited code

    if (!function_exists('wp_generate_attachment_metadata')){
            require_once(ABSPATH . "wp-admin" . '/includes/image.php');
            require_once(ABSPATH . "wp-admin" . '/includes/file.php');
            require_once(ABSPATH . "wp-admin" . '/includes/media.php');
        }
         if ($_FILES) {
            foreach ($_FILES as $file => $array) {
            $mime = $_FILES[$file]['type'];
            $filesize = $_FILES[$file]['size'];
            $maxsizef = 524288;
            if($filesize > $maxsizef) $error_array[] = 'error size, max file size = 500 KB';
            if(($mime != 'image/jpeg') && ($mime != 'image/jpg') && ($mime != 'image/png')) $error_array[] ='error type , please upload: jpg, jpeg, png';
                $attach_id = media_handle_upload( $file, $post_id );
            }   
        }
        if ($attach_id > 0){
            //and if you want to set that image as Post  then use:
            update_post_meta($post_id,'_thumbnail_id',$attach_id);
        }

it’s work.