Using a hash of what you are hashing as a salt?

Question

Say a user registers for your site, you hash the password they have chosen then use that hash as a salt and rehash their password with that salt.

Example:

Answer 1

This is key strengthening (http://en.wikipedia.org/wiki/Key_strengthening), a nice technique that nonetheless does not substitute for actual salt. It will not protect you against a rainbow table written with this double-hash function.