I would like to know whether there's any unique id with which we can distinguish files in Dropbox. Because when we copy/move a file in dropbox,it is detected as a new change by delta api. And it would be good if we can distinguish files in dropbox with a unique id. I've done some research and didn't find anything. So any help would be appreciated.
Yes, Dropbox API v2 does now offer file IDs that persist across moves/renames. You can find more information under "Path formats" in the documentation.
The file ID is available as the id field on the FileMetadata object, e.g., as returned by /files/get_metadata.