Answer:
newspaper and newscast probably have credentials and registered as a news business, blog is probably just someone normal reporting it. from nppa website, you don't need government approval to work as a journalist but press credentials related to news coverage are usually issued by law enforcement agencies. and event specific press credentials are usually provided by the organizers of the event. if you just blog about it and just look for everything online, you won't really need press credentials unless you want to do field work