If an image in the Image bank under Publish > Media > Image bank is shown with a button that says PUBLISHED, this means that this image has been published in the Media library, i.e. under Media library in your public newsroom.

If an image in the Image bank under Publish > Media > Image bank shows a button that says IN USE, this means that this image is being used somewhere outside of the Media library, e.g. in a press release. The image can at the same time be published in the Media library, but not necessarily, as it may just have been added as the header image or in the body text of the press release.

To sum up, PUBLISHED means that the image has been published in the Media library, whereas IN USE implies that the image is being used outside of the Media library.

• Do you want to remove an image completely (e.g. clean up images that are neither published nor in use)?
  Click on one or more images in the Image bank (under Publish > Media), and delete via the trashcan button that appears to the upper right.
• Do you want to remove an image from the Media library, without it getting removed from other places where it’s being used?
  Click on one or more images in the Image bank (under Publish > Media), och use the Edit button. At the upper right corner you will see the settings for ”Newsroom media archive status”. Update the status from Published to Draft, and save your changes.

Please also see:
In which ways can I add images to my press release?
Publish an image