Disclaimer: I am not a lawyer, I am a photographer.
In today's world it is hard to look around without seeing something that has been copyrighted. When pointing the camera lens somewhere, it is just as hard to avoid capturing the image on film.
The first is 'what may be protected by copyright?' This covers any original work of art. If you can see it, it may be copyright. Statues, fountains,
buildings (younger than Dec 1, 1990 - more on this below), advertising signs, toys, etc. At first this may seem crippling to a photographer, however there are limits on the reach of copyright.
The two parts of copyright law that let photographers are that of fair use and de minimis. When considering does a photograph infringe three questions may be asked:
It is not necessary that an object be in perfect focus to constitute a copy. Nor must the entire work be in the photograph for it to be a copy. The question here one of "is the object in question recognizable by a lay person?" It is important to remember that the object may be only a small fraction of the photograph, or only a small fraction of the object be in the photograph - but if it is recognizable, it may be considered infringement. See also Copyright and Old Masters for a court case regarding photographs of a replica of a work no longer protected.
Just because the photograph is a different medium than the object in question (say, a sculpture or a choreographed dance) a photograph may still be considered an infringement. These cases would have the photograph be a derivative work of a preexisting work.
While a taking a photograph of Half Dome from Sentinel Bridge (given the popularity of that spot some must think that it is the only place to take a picture of Half Dome) does not infringe upon the copyright of others even though thousands of photographers have been there before. On the flip side, deliberate replication of major elements of the photograph may be a copyright if the images are "substantially similar". However, there are no clear boundaries on what "substantially similar" means. Courts have often left it up to the jury as to deciding if two photographs are similar.
De minimis when applied to copyright is about courts
refusing to waste time on trivial matters. This is not clear cut either. Some decisions have suggested that anything for purely private use (a web page is not purely private use) may qualify as de minimis - though this is not explicitly defined. Realize it is up to the court to decide
if the issue is de minimis or not - not the photographer.
Fair use is a word that comes up often within copyright matters. In these cases, the issue is often one of what is it being used for? A photograph for non-commercial use is more likely to be considered fair use than one that is used for commercial gain. This is especially the case when the photograph serves the same purpose as the original - a fine art photograph of a sculpture would not be considered fair use.
Another key question is what does the photograph do to the market value of the copyrighted work? This is most likely the key question when considering fair use (the others being intended use (discussed above), nature of work, and amount of work copied - the later two do not weigh heavily into as use and value with respect to photographs). It was ruled that a magazine copy of fine art postcards does not reduce the value of those post cards (it is not suitable for those buying post cards or collecting fine art).
Buildings fall in a special category when it comes to copyright. The building itself may be copyright - the building in context of the skyline may not. However, there is an explicit exception that allows anyone to take and distribute photographs of a building that is viewable from a public place. This exception does not extend to the interior of a building. Furthermore, monuments are protected as sculptural works. There are some buildings (post offices and military instillations) that may not be photographed in any case. Realize that the ornamentation on the building may be protected by a separate copyright that is not expected - the classic example being the sculptures of lions at the New York City Library. Furthermore, some cities have local ordinances restricting photographs, often permits are required in cases of commercial photography.
Realize that many copyright owners protect their property with vehemence. While a photographer may think "they should appreciate the free publicity", many do not place any value on the publicity while others are grateful for the publicity and the opportunity extract some money from the infringer. A compliment does not protect the photographer from damages and legal fees.
Legal Handbook for Photographers Bert P. Krages, Esq.