A few of the settings for image fields are defined once when you create the field and cannot be changed later; these include the choice of public or private file storage and the number of images that can be stored in the field. The rest of the settings can be edited later; these settings include the field label, help text, allowed file extensions, image resolution restrictions, and the subdirectory in the public or private file storage where the images will be stored. The editable settings can also have different values for different entity sub-types; for instance, if your image field is used on both Page and Article content types, you can store the files in a different subdirectory for the two content types.