Why not use Gravatar/Libravatar/... ?¶
Various people asked or complained about the generated icons next to their comments. First, it is not an avatar, it is an identicon used to identify an author of multiple comments without leaking personal informations (unlike Gravatar).
Although partially answered on the index page, here a more complete answer: If you manage massive amounts of comments, Isso is a really bad choice. Isso is designed to be simple and easy to setup, not optimizied for high-traffic websites (use a dedicated Disqus instance then).
comments are not big data
For example, 209 threads and 778 comments in total only need 620K (kilobyte) memory. Excellent use case for SQLite.