Add css class in get_webcomic_media()

Hello!
I wish to know if there is a way to insert css classes in the tags generated by the get_webcomic_media() function. I used a method to get around the problem:

$string = get_webcomic_media();
$string_replace = str_replace( “native-class”, “native-class my-class”, $string_replace );

Is there a way within the webcomic to do this?
Thanks and sorry my english if something is wrong.