Jurors typically judge for technique, subject, and meaning. While the ultimate decision is left up to the juror, there are certain guidelines that are followed. Artwork is kept to a family-friendly nature (no nudes and/or explicit imagery will be accepted).
Artwork is also expected to be adequately photographed. The photo doesn’t have to be perfect, but it does have to reasonably show the artwork without editing on our part. Artwork meant to be rectangular should still be rectangular in the photo.
Also, duplicates of existing work are not permitted, whether the original is in a museum or on a magazine cover. Simply duplicating existing work is wrong.