Walrus is a storage service included with Eucalyptus that is interface compatible with Amazon's S3. Walrus allows users to store persistent data, organized as buckets and objects (see Amazon's S3 Getting Started Guide for more information). Walrus system options can be modified via the administrator web interface.
If you would like to use Walrus to manage Eucalyptus VM images, you can use Amazon's tools to store/register/delete them from Walrus.
Otherwise, you may use other third party tools to interact with Walrus directly.