Individual members who are moderated by flagging the account for moderation will be moderated everywhere throughout the community, however, to ensure that all files or comments are moderated within a specific media gallery regardless of the author's account moderation status, you can enable moderation directly by navigating to the media gallery, Manage > Manage Gallery > File Options:
To moderate files, check the Moderate Files checkbox. To moderate comments made within this media gallery, check the Moderate Comments checkbox. If you've made any changes, be sure to click Save to commit them.
When moderation is enabled, files and comments in the gallery will then go through the moderation workflow.