Any edit replacing a tagged image with a non-tagged image will be reverted.
Just a legal tangent.
Now, for images we use on the wiki, we use images under fair use and fair dealing laws. These laws can protect a limited use of official images but there are restrictions, and to comply properly all images we upload should be tagged with proper fair use information using fair use.
Images should ideally be formatted using the |Information template.
Always specify on the description page where the image came from, such as a URL (for official websites), or the name of the source from which the image is scanned or captured. Don't put credits in images themselves.
Use a clear, recognisable, non-duplicated filename. Note that if any image with the same title has already been uploaded, it will be replaced with your new one.
Do not upload content with false descriptions, sources, or copyright tags. The image will be deleted.
Images should be of the highest quality possible; in the case of duplicate images, the highest quality image is kept.
Never upload .gif images, and don't bother converting a .gif into another file format before uploading. We do not need animations, and the .gif format does not handle quality properly. It has a limited colour depth, and as a result the moment you save an image with the .gif format, it loses a large amount of quality. We also prefer .png images over .jpg images because .jpg images slowly lose quality each time you save them. Neither of these types of quality loss can be recovered without the original image.
When placing an image inside of an article, never use px sizing. Instead use a |thumb|right| or |thumb|left|. Using px sizes overrides user preferences on the sizing of thumbnails and makes things inconsistent, so we avoid the use of it. The only exception to this rule is for special images locations and icons. Such as the icons in templates and images in infoboxes which require a specific size to be flush with the infobox.