Perhaps this post by @nraboy may help https://blog.couchbase.com/storing-base64-files-directly-in-couchbase-via-nodejs/ .
W.r.t. modeling your data, with pre-encoded base64 images, you could (a) store the images as JSON values within your document itself or (b) maybe store them as separate JSON documents referenced by the parent document. @nraboy may be able to offer other ideas.
As a side, the decision on whether you store the images directly in the Database or in a separate file system is a choice you would have to make depending on your application needs (image sizes, storage cost, replication).