"local" comment avatars without being a wordpress user?

Hello – I am new to the whole avatar thing and trying to learn about all this. I am aware of the gravatar service and also installed the “add local avatar” plugin. That plugin allows wordpress users to upload a local avatar. My question is this; is there any plugin that we can have that will allow a commenter to upload a local avatar for our site without them being a wordpress user? I know gravatar can do this but I am wondering if there is anything that can do it just when they are on our site? Or do they have to be a wordpress user?

Thanks,
Gerard