Official screenshots from the Doom game page (GBA version)
Preview screenshots released by id Software in downloadable form on 5 October, 1993.
Screenshots published on the Doom Companion CD-ROM by Limelight Media, Inc., showing a pre-release version of the game (possibly the Press Beta). The date stamps on the files are from 14 November, 1993. A note in the same folder states that the screenshots are unofficial but their origin is not specified.