I am summarizing here some rules what consists of acceptable image use in scientific publications (Rossner 2004). Pioneers in the field have been the Journal of Cell Biology (J) but also Nature (N) and EMBO Press (E). Here are 10 rules:

1. Digital images submitted with a manuscript for review should be minimally processed (N).
2. Specific feature within an image may not be enhanced, obscured, moved, removed, or introduced (J, E). The use of touch-up tools, such as cloning and healing tools, or any feature that deliberately obscures manipulations, is unacceptable (N).
3. Dividing lines may not be added between juxtaposed images taken from different parts of the same gel or from different gels, fields, or exposures (J, E). If juxtaposing images is essential, the surrounding gel shown at least at the size of the band, borders should be clearly demarcated and described in the legend (N).
4. Images gathered at different times or from different locations should not be combined into a single image, unless it is stated that the resultant image is a product of time-averaged data or a time-lapse sequence.
5. Adjustments of brightness, contrast, or color balance that have been applied to the entire image may not enhance, erase, or misrepresent any information present in the original, including the background (J, E).
6. Images from the same object may not be repeated within the manuscript. Any reuse of images, including control images from earlier papers, should be explicitly stated and justified in the legend (J) as reuse would pretend any independent evidence. Reprobed Western blots should be clearly indicated.
7. Nonlinear adjustments (e.g., changes to gamma settings) must be disclosed in the figure legend (J). Processing such as changing brightness and contrast is appropriate only when it is applied equally across the entire image and is applied equally to controls. Contrast should not be adjusted so that data disappear (N).
8. Excessive manipulations, such as processing to emphasize one region in the image at the expense of others, is inappropriate (N).
9. Deposition of all RAW image files is encouraged (N). An option is figshare.com that is available since 2014.
10. There should be a better distinction of object and  image, e.g. the re-use of the same object in multiple images should be banned. With any additional image in a paper, this is assumed to be additional and independent evidence of a given fact. Exception of that rule is a clear label (box, arrows, letters) as well as a legend why and from where it has been taken from (J).

These are general rules only.  Specific rules exist for electrophoretic blots and microscopy (N). Additional points

• There should be a reference to any work outside of the current paper, if the object and/or image has been used elsewhere.
• There is a need for better captions that specify always experimental conditions, object, direction and resolution. Unzoomed controls and reason for the selection of certain object areas along with repeated experiments would be often helpful. The question is largely unsolved what constitutes a representative image?
• There is a need of professional integrity offices at universities and research centers.
• More attention by publishers is required. The Committee on Publication Ethics (COPE) guidelines include a flowchart on suspected image manipulation.
• Accepted standards and current practices need to be continuously revised.

As a further reference see also the Word Press Photo rules.

Postscript 4 Jan 2022

OSF Initiative by Joris van Rossum