Avatar plugin that randomly selects avatar from pool of images/changes color?

Does anyone know of any plugins that allow you to load a selection of images into a directory and it randomly assigns them to posters who don’t use Gravatar, based on identifying information (their email address)?

I don’t want to use the *same* static image for posters without Gravatar images, but somehow to provide posters with different images which are still related to the theme of my business.

I’ve experimented with the “generated” options that come with WordPress by default (Identicon, Wavatar, MonsterID and Retro) but they are too generic and I want them to relate to the theme of my business.

ALTERNATIVELY…

Are there any plugins which can randomly change the color of a default avatar image that I provide (again, based on the posters’ email addresses). For example, you could use an image of a car as the default avatar for non-Gravatar users… and each person’s car avatar would automatically appear as a different color, based on the email address they provide when posting their comment.

Any ideas? Thanks!