Is it possible to “reverse engineer” identicons?

As shown in this question, default user avatars (like mine) are identicons and are generated with the user’s email (where provided) or the user’s IP address (where the email is not provided).

Given any identicon and information of whether it was generated from an email or IP address, can the email or IP address be identified? If yes, post my email in a spoiler (I registered an email with my account). If no, provide reasoning why.