This is primarily for the banner sidebar whenever you use the Image Widget. If your image has a caption when displaying this widget, you can show or hide the caption.

With the image caption
Without the caption
  1. Go to Appearance > Customize > Other Options
  2. Look for the Hide Banner Captions setting and toggle it to turn blue (disables it).
  3. Click the Publish button.
screenshot showing the hide banner captions setting