Making an image appear

Hey I need to make an image appear when

 public void CompareGuesses (string guess){
     if (guess.ToLower() == gameName.ToLower()) {
         SceneManager.LoadScene("Level 1");

When this script gets activated, the image is called "ArmyOfTwoImage" The image needs to be invisible until the "CompareGuesses" is called. Then it needs to become visible and cover up a button. Thanks in advance :)