So, first to give you a technical answer to your question, check out the cbc tools which are distributed with libcouchbase. There is an older blog which intros them.
One of those is
cbc cp, and using it you can “copy” a binary into a binary item. You can technically do that with an entire directory of binaries. The source is available, of course. All of the SDKs also support loading such binary items.
Now, having said that, you probably need to think through this a bit more from a data access perspective. Do you need to store the file/mime type? Are you going to need to get any metadata without accessing the entire binary? Things of that nature.
cbc cp just loads the data and the filename. It meets the strict definition of what you’re looking for, but you’ll probably need something more in most cases.