returns posts authored by a comma delimited list of authors id’s or a single id.
[featured_image_pro author__in='7,8' subcaption1='author' orderby='author']
returns posts that are not authored by a comma delimited list of authors id’s or a single id
[featured_image_pro author__not_in='7' subcaption1='author' ]
returns posts that are authored by the user name.
[featured_image_pro author_name='user1' subcaption1='author']