Wikipedia:What is a featured picture?/Examples of technical problems
There is no agreed definition of what constitutes a featured picture. However, Wikipedia featured picture candidates should not display any of the following technical flaws, unless there are strong mitigating reasons, such as historical significance or unique subject matter: see the featured picture criteria page for guidelines, and the WP:WIAFP/example subject matter gallery for examples of notable exceptions.
Image quality problems
Over-exposed, undesirable motion blur, main subject partially obscured and out of focus Blown-out highlights due to high-contrast lighting.Top: original image.
Bottom: blown-out areas marked red
Example of excessive image noise (grain) due to a high sensitivity (ISO) necessitated by poor lighting.
JPEG compression, colour fringing and post-processing artifacts
Purple fringing, a form of chromatic aberration. See here for a closeup.
Focus, content and composition errors
Main subject not entirely in focus (depth of field too shallow) Even a small tilt is noticeable. Editing the image may fix the issue.
Typically, technical problems in nominated images aren't as blatant as they are in the examples above. Here are some real world case studies.
|Wikipedia:Featured picture candidates/Oklahoma City memorial||Stitching errors, white building overexposed, posterisation (probably caused by JPEG compression), slight chromatic aberration, inappropriate file type|
|Wikipedia:Featured picture candidates/Two JFKs For Father's Day||Film grain, out of focus, oversharpened, smallish|
|Wikipedia:Featured picture candidates/Blue Manakin||Noise, subject not entirely in focus (insufficient DOF)|
|Wikipedia:Featured picture candidates/Snail climbing grass SMC 07.jpg||Insufficient DOF, JPEG artifacts|