Currently Atticus primarily focuses on text formatting and book layout rather than image manipulation. Therefore, it offers limited options for making specific image adjustments within the platform.
Opacity settings are only available for background images used in the chapter header. If this is the setting your are looking for, it can be found in your theme settings.
You can make changes to your theme on the Formatting Tab by clicking the three dots next to the theme name and selecting Edit or Edit as New Theme.
For more details on how to set up or adjust your theme settings, you can refer to this tutorial: https://www.atticus.io/create-a-custom-theme/ It provides detailed instructions and tips on creating and modifying your theme.