If you use simple encoding (e.g. uncompressed bitmap), your archival capacity will be extremely limited, esp. if you use low-density medium (optimized for longevity). There's an obvious trade-off between encoding complexity and how much can you archive.

One approach would be to have a layered strategy - simple (but inefficient) encoding for an initial set of data, accompanied by a bootstrap for the next level which would unlock access to a much larger collection of efficiently stored data.