What identifies a case in this area?
It is important that every author of a contribution be credited as such. It is equally as important that a person not be named as an author when he or she is not.
Ghost, guest or gift authorship
A ghost author is someone who is omitted from an authorship list despite qualifying for authorship. A guest or gift author is someone who is listed as an author despite not qualifying for authorship .
Test for authorship
Authorship is not a clearly defined concept. To be an “author” one must have responsibility for a particular aspect (that is not minimal) of the research or preparation of the work, that is, must have made a significant contribution to the conception, design, execution, or interpretation of the reported study, and must have approved the final form of the work. Fundamentally, an author must be prepared and have the ability and responsibility to publicly defend the work.
You may wish to use the following standard as a test for authorship: All Authors of a paper have the ability and responsibility to publicly defend that paper. A trivial contribution would not be sufficient to confer the status of author. Lesser contributions to a work can be recognized by clearly crediting such person as a “contributor,” rather than an “author.”
An author submitting an article is required to identify all co-authors and any other contributors (and to obtain consent from them for the publication of the article). Where necessary, you should seek clarification from authors and contributors to establish exactly who has done what in relation to the article and the research. You should require that all those who satisfy the test of authorship outlined above are in fact credited as co-authors.
 Source: Committee on Publication Ethics, ‘How to spot authorship problems’, 2008.