Embedded overlays are overlays created by third-party systems (such as the imaging modality), and encoded in the image object. When applied to an image, the corresponding image pixel is replaced by an overlay pixel. When combined with other overlay pixels, the graphic is displayed over the image. Overlays can exist for any object, but are frequently found on summary or localizer images.
By default, overlays are displayed if they exist for an object. To toggle the overlay setting, press Alt-F9, or click View/Show Overlays.