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In Drupal 7, while attempting to specify the "File directory" option as "fields/field_foo/[node:nid]" in an image field configuration, the form does not validate. The error text is: "The File directory is using the following invalid tokens: [node:nid]".
As per File (Field) Paths, core does not support node tokens for this. This is a feature request to get this into core. It will greatly help folks keep their "files" directory clean.
Also see ImageField Tokens.