Documentation on how to use UUID?

Perhaps I missed it some where but is there some documentation on how to use this module?

We are very interested in this module because we have multiple sites representing a biological image repositories and need unique identifiers between sites. I played around with the module a little, but wondering how to achieve certain things.

For example:
We have an Image node whereby a user uploads and image with some information pertaining to that image. During the submission process of the node form, I wrote some custom functions after the node is saved to process the image to a remote image server. I first grab the image info using:

$image_info[$fid] = file_load($fid);

I am then going to send the image to our scripts on the remote image server using CURL for processing. I would like to use the UUID for the image... or is it better to use the node UUID?... for naming the image on the remote image server.

So how do I obtain the UUID for the file or node?
I assume I can then use the UUID later using the services?
I would just like some ideas or documentation to help me a long the way.

Thank you