I'm already using gravatar icons for the users of my web service. However, I'm finding several problems with this approach:

• Only a small percentage of the users take the time to set up a gravatar profile. My users are not tech-savvy, but would be likely to add a dedicated photo to my site.
• Users of my service are encouraged to use images that depict them in proper uniform for the industry my service relates to. They wouldn't want that same picture to be used for personal purposes throughout the internet.
• They would not take the time or effort to manage a separate email address and gravatar account just to have an "in-uniform" profile photo for my service.

Before I implement my own profile image feature, I was wondering if there are any open-source solutions that I could leverage with similar features to gravatar. Specifically:

• The ability to display any size thumbnail (up to 512px would be fine)
• Takes care of caching different sized thumbnails
• Has support for something like identicons, preferably pluggable with different style algorithms (monsters, etc.), even better if I can customize these
• Ability to fall-back to gravatar if no photo found

Does anything like this exist? I haven't found it yet if it does.