Wikipedia:Choosing appropriate illustrations

This page has a few suggested guidelines for choosing the type of illustration that would be most appropriate for various circumstances. Many times, a Wikipedia article needs an illustration, but it is not immediately clear what kind of illustration is needed. Should it be a photograph or a drawing? Should it be detailed or simple? You are not obligated in the least to follow these suggestions, but you may find them useful in choosing what kind of image to use for a particular article.

This page was originally conceived as part of WikiProject Illustration.

Classifying images

Images on Wikipedia can be loosely classified according their nature or origin:

Photographs

Any real-world scene captured using a camera or other photographic technique

Diagrams

Any manually or automatically created drawing, instructional picture, or conceptual illustration

Computer-generated renderings

Any image generated by a computer based on some input data or scene description language

Artwork

Digitally replicated works of art, including paintings, sketches, or other typically two-dimensional media

While these classifications often overlap (artwork may be replicated by photographing it; diagrams may be computer-generated; photographs may be works of art, etc.), they may serve as conceptual niches in determining the appropriate format for a visual illustration.

Image purpose

Images serve a number of different purposes within articles. The following details several broad categories of image "type", and lists situations in which each type may be most appropriate.

Appearance

Some images serve primarily to show the appearance of something. Images used within Wikipedia articles most often serve this purpose. Portraits or photographs of persons; photos of real-world objects taken primarily to show their visual appearance; diagrammed variations of characters in an alphabet; all serve the task of communicating the visual attributes of some subject.

If your article needs an illustration mostly for the purpose of showing what something or someone looks like, an appearance-oriented image is probably the best option. Many times, photographs are the best way to achieve this; however, in some cases a photograph is unavailable, for example, if you are seeking an appearance-oriented image of George Washington, a painted portrait may be the most appropriate alternative. For showing the appearance of something which cannot be photographed for some reason, for example, the letter A, a drawing may be best.

Structure

Illustrations with labels, highlighted components, or other selective or stylized attributes often serve the purpose of demonstrating the structure of something. A map showing the political boundaries of a country, a diagram of the inner workings of a clock mechanism, or an illustration of the structure of a binary tree may fall within this classification. Examples of this type of illustration include those shown in several varieties of lock, in Enigma machine, and in Data Encryption Standard.

If your article needs an illustration for reasons of showing structural attributes, this type of image may be what you need. In these cases, the appearance of the subject is not as important as the way it is organized or how it works. Most often, a drawing or diagram may be most appropriate for this type of image, but in other cases an annotated photograph may be a viable alternative as well.

Concept

Images often serve to illustrate a concept. Some images may be used primarily to demonstrate abstract conceptual material in a visual way. A digitally tinted photograph may be used to demonstrate the concept of hue or saturation; the graph of two mathematical functions could help to show how functions may relate to one another; a diagram could show a physical process such as heat dissipation or magnetism. Examples of this type of illustration can be seen in dithering and HSV color space.

If your article needs an illustration primarily to demonstrate a concept that cannot be easily described in another way, this type of image is probably a good choice. A conceptual illustration may often take the form of a diagram, but other formats may be appropriate in some cases too.