Any original content is fine.
If you create a graphic from scratch, write text from your own imagination, or create an original audio or video recording, you can put these on your web page without worrying about copyright. However, you may want to ensure copyright protection on your original material. The trick is knowing what is in the public domain. Remember that these are not hard and fast rules. If you are in doubt as to whether material is in the public domain, ask for permission to use the material.