How to compare images?

Question

For a project I am making a memory game, but I am trying to make to objects disappear when the are equal. This is my code:

public void opencard(){
    int duiker = 0;
    int duiker2 = 0;
    if (duiker == duiker2){
        if(Greenfoot.mouseClicked(Duiker.class)){
            setImage("duiker_tcm46-175501.jpg");
            if(Greenfoot.mouseClicked(duiker2)){
                duiker2 = 1;
            }

            duiker = 1;{
                getWorld().removeObject(this);
            }
        }
        else if(Greenfoot.mouseClicked(this)){
           setImage("duiker_tcm46-175501.jpg");
           Greenfoot.delay(150);

          setImage("150px_RGB_WEBSAFE_D_B_G_26-29652.gif");
        }
    }
}

But they disappear even when I don't click on them.