You can't add an image to a Text Area. You can add an image to a JTextPane and/or a JEditorPane. You can find tutorials on this
here and/or you can use the Search feature on this forum because this has been asked many times in the past.
Another approach you could do is you could add an image to a JLabel and place it above or below the TextArea. Not sure if that is the look you are going for. My first suggestion is your best bet if you need anything between words/sentences in your TextArea.