Wikipedia:Featured picture criteria

A featured picture:
 * 1) Is of a high technical standard.
 * 2) * It has good contrast, accurate exposure and neutral colour balance.
 * 3) * It shows no significant compression artifacts, burned-out highlights, image noise ("graininess") or other processing anomalies. Examples of common technical problems can be found here.
 * 4) * Its main subject is in focus, it has good composition and has no highly distracting or obstructing elements.
 * 5) * Exceptions to this rule may be made for historical or otherwise unique images. If it is considered impossible to find a technically superior image of a given subject, lower quality may sometimes be allowed.
 * 6) Is of high resolution.
 * 7) * It is of sufficiently high resolution to allow quality print reproduction. Still images should be a minimum of 1500 pixels in width and height (1500×1500px); larger sizes are generally preferred. The size of animated images is judged less strictly, though larger is still preferred. Further information on image size can be found here.
 * 8) ** Exceptions to this rule may be made where justified on a case-by-case basis, such as for historical, technically difficult or otherwise unique images, if no higher resolution could realistically be acquired. This should be explained in the nomination so that it can be taken into consideration.
 * 9) ** Note that vector graphics in SVG format omit any requirement for any pixel count.
 * 10) ** Animations and video may be somewhat smaller.
 * 11) Is among Wikipedia's best work.
 * 12) * It is a photograph, diagram, image or animation which is among the best examples of a given subject that the encyclopedia has to offer.
 * 13) * It illustrates the subject in a compelling way, making the viewer want to know more. A photograph has appropriate lighting to maximize visible detail; diagrams and other illustrations are clear and informative.
 * 14) * A featured picture is not always required to be aesthetically pleasing; it might be shocking, impressive, or just highly informative. Highly graphic, historical and otherwise unique images may not have to be classically beautiful at all. See these examples for a basic guide.
 * 15) * commons:Help:Scanning offers advice on preparing non-photographic media (engravings, illustrations from books, etc) in your possession for Wikipedia.
 * 16) Has a free license. It is available in the public domain or under a free license. Fair use images are not allowed. To check which category a particular image tag falls under, see the list at File copyright tags.
 * 17) Adds significant encyclopedic value to an article and helps readers to understand an article.
 * 18) *The image is used in one or more articles. It is preferable to wait a reasonable period of time (at least 7 days) after the image is added to the article before nominating it, though this may be ignored in obvious cases, such as replacing a low-resolution version of an image with a higher resolution of the same image.
 * 19) *A picture's encyclopedic value (referred to as "EV") is given priority over its artistic value.
 * 20) Is verifiable. It is supported by facts in the article or references cited on the image page, or is from a source noted for its accuracy. It is not created to propose new original research, such as unpublished ideas or arguments.
 * 21) Has a descriptive, informative and complete file description in English. A complete file description:
 * 22) *Properly identifies the main subject, including Latin and technical names where applicable.
 * 23) *Describes the context of the photograph, painting, or other medium. Geotagging photographs of identifiable places is encouraged. This entails providing the coordinates of where the camera was when the medium was recorded to an appropriate degree of precision no less than ~10 km² (see Commons:Geocoding, or Template:Coord if the image is hosted on the English Wikipedia).
 * 24) *States the most relevant meta-detail (such as date, location, event, version, etc). It is suggested that additional relevant information that becomes known during the course of the nomination be subsequently included in the file description.
 * 25) *May include languages other than English but there must be an English version available that meets this criterion. The file name may be in a language other than English.
 * 26) Avoids inappropriate digital manipulation.
 * 27) *Digital manipulation for the purpose of correcting flaws in a photographic image is generally acceptable provided it is limited, well-done, and not deceptive.
 * 28) *Typical acceptable manipulation includes cropping, perspective correction, sharpening/blurring, and colour/exposure correction.
 * 29) *More extensive manipulation should be clearly described in the image text.
 * 30) *Any manipulation which causes the main subject to be misrepresented is unacceptable.
 * 31) *Note that this criterion is not relevant to vector-based SVG images, as the entire image is a digital construction.

Improving image quality
See: How to improve image quality

Examples of image problems
See: What is a featured picture?/Examples of technical problems