Certain preference settings cause Mathematica to return the text “–Graphics–” instead of an image. To fix these settings, first go to the Preferences dialog:

  • On Windows and Linux, navigate to Edit ► Preferences
  • On Mac, in the toolbar, navigate to Mathematica ► Preferences

Once in the Preferences dialog, click the Evaluation tab. Adjacent to Format type of new output cells, click the drop-down menu and change the value to StandardForm.