If an artist draws a picture of some famous political figure, who owns the copyright to that image/drawing - the artist or the political figure in the drawing?
What if the artist drew a picture of the political figure in a famous setting (such as a president by his inaugural address) - does that effect anything?
Similarly, what if the artist simply copies a famous scene that was taken with a digital camera and converts it to an almost identical drawing?
The artist is always the initial owner of the copyright unless, under US law, the artist was hired to do the drawing under circumstances which make it a "work made for hire". This requires a regular employment relationship, or an explicit written contract saying that it is for a work made for hire. In the US this makes the employer the original owner, and then legal author. That is not true in most other countries. In many countries the natural person who creates a work is the author, even if by contract the copyright is immediately transferred to the author's employer. This matters because the author's life is used to measure the copyright term. In the US a work-made-for-hire has a fixed term (of 95 years from publication, or 120 from creation, whichever ends sooner), not measured by anyone's life.
However, once the work has been created, the artist may sell or give away the copyright, including to the subject, if s/he so chooses.
However, although the subject does not normally own the copyright, the subject may have relevant "rights of publicity" which may limit what the artist can do with the drawing. In particular, using it to advertise anything may be unlawful unless the subject's permission is obtained. Whether such rights exist at all, and exactly whatn they cover, varies significantly by jurisdiction. Inn the US this varies by state.
The author is the initial owner of the copyright, and when the work is made for hire "the employer or other person for whom the work was prepared is considered the author." See 17 U.S.C. 201
This is true for any "original works of authorship" including "pictorial, graphic, and sculptural works" (17 U.S.C. 102) no matter whether it was a political figure in a famous setting or whether it is based on a scene observed in a digital image.
Your final question contains a complexity though: the drawing that almost identically copies a photograph might not be original; it might also be an infringment.
The answer in Canada is the same, subject to a distinction between initial authorship and ownership.
The "author of the work" is the initial owner of the copyright (Copyright Act, s. 13(1)) unless the author of the work was in "the employment of some other person under a contract of service or apprenticeship and the work was made in the course of his employment by that person" in which case, absent some alternative agreement, the first owner of the copyright is the employer (s. 13(3)).
The Berne Convention also indicates that copyright protection "shall operate for the benefit of the author." So any signatory that is implementing the Berne Convention will vest initial copyright ownership in the author.
In the first two cases, the artist owns copyright, as stated in this Q&A (replace "photographer" with "artist"). In the third case, the artist owns the copyright to his creation, but has also infringed the copyright of the photographer (it does not matter what kind of camera it is). However, if the picture was taken by an automatic camera that takes a picture at random without any originality, the photo is not copyrighted so there is no infringement.
Broadly speaking, copyright is a reward for creative expression. A painter will generally hold copyright for their paintings, since they are making creative decisions about what and how they are painting. Similarly, a photographer will express creativity through a choice of angles, composition, lighting, exposure settings, and so on.
If a painter reproduces a scene from a photograph, it is likely that the painting will be a derivative work of the photograph – containing copyrightable aspects from both the photographer and the painter. However, it is possible that the painter does not contribute any copyrightable authorship of their own. The author of the original can generally decide whether creation of derivative works are allowed.
The subjects of a photo or of a painted portrait do not contribute any creative expression to the work, and are therefore not a copyright holder. However, there are a variety of different rights that could play a role. For example, the subject might have personality rights that could affect whether the work may be published, but that right might not weigh very strongly for public figures. The owner of the physical medium (e.g. of the painted canvas) has some rights in that object.
All of these rights and their interplay are quite jurisdiction-dependent. In the United States, the US Copyright Office has published a series of circulars and a compendium that discuss details of the US copyright system. For example, section 905 of the compendium discusses when works of visual arts (including paintings and photographs) might be copyrightable.
