Is there a tem­plate tag that just gives plain text rather than a link to the au­thor page for users of my blog?

Yep! If you would pre­fer plain-​text rather than a link for all me­dia cred­it (and leav­ing out the sep­a­ra­tor and or­ga­ni­za­tion), call <?php get_media_credit($post); ?> which us­es the same pa­ra­me­ter as above. To echo the re­sults, call <?php the_media_credit($post); ?>.