If you’re a LiveJournal user, and you want your LJ picture to come up when you comment on my blog (and don’t have a Gravatar), enter your email address as <lj-user>@livejournal.com. This will display your LJ default picture instead of asking Gravatar for your picture/avatar.

If you’d rather use your real email address, you should head over to Gravatar and register, uploading your pic there.