With photos, videos, etc., there's not a lot of duplicate information. If there are a lot of new images being created, then you'll see very little benefit from data deduplication. In that case, you're better off just running differential or incremental backups.
As far as areas in which data deduplication can provide superior benefits, databases have a lot of redundant data and deduplication can have dramatic results. Also, large file systems with small numbers of changes are a good match for deduplication.
Check out the entire Data Deduplication FAQ.