There are several different ways to handle visual identities online, but none so far have captured my interest (except perhaps one). My website, for instance, currently outsources to Gravatar.com, which means that people who both comment on my website and have an account at Gravatar.com will have an image show up next to their name.
Gravatar.com's big draw is that the members' images are all moderated, so I can restrict images to only those that are rated 'G', or 'PG'. The problem is that their images seem to load slowly, and (as I and others have found) it seems to take a very long time for new images to be rated and approved. What I would like to see is a decentralized service, preferably using URLs instead of email addresses.
I've disliked the idea of uploading an image at each and every service I sign up for, such as Flickr, Digg, Last.fm, AIM, Yahoo, MSN, ICQ, Google Talk, Jabber, Xanga, MySpace, Facebook, LiveJournal, Blogger, et cetera. This clearly makes visual identity consistency enforcement a daunting task. (My, but that last sentence was a little too wordy!) Nonetheless, I recognize the importance for these services to centralize user images. Thus, I'll focus only on the visual identity of comment authors on my blog.
There are only two other schemes that I've found that could potentially replace gravatars, and those are favatars and Pavatar. Favatars are a simplistic worst-case solution in my opinion, and Pavatar has absolutely no implementations anywhere. Of the two, Pavatar seems to be the most promising, but it also appears to be a very underdeveloped concept...maybe I should offer to help with the English translation? Regardless of its current state, the Pavatar specification comes pretty close to my optimal solution: I publish an image to my website, and that image is then picked up all across the internet whenever I input my website URL - I am, after all, a big fan of decentralization!
Until I have a better solution, I'll probably just keep using Gravatar.com, although I would like to one day extend my blog software so that people who haven't signed up for a gravatar will have their webpage checked for profile pictures, such as those found at Blogger, LiveJournal, and Xanga.