not used it but BeginHUD sounds like it's the right thing (HUD = head up display)

http://mrfeinberg.com/peasycam/reference/peasy/PeasyCam.html#beginHUD()

documentation lacking somewhat, probably best to look at the code for examples.

Thanks koogy! I combined what you said with my idea and I got this, which seems to be working fine now.

  hint (DISABLE_DEPTH_TEST);
  cam.beginHUD();
  noLights();
  if (worldnum == 2) { 
    image(legends[0], width-320, height-108);
  }
  else if (worldnum != 1 && worldnum != 2) {
     image(legends[1], width-320, height-108);
  }
  cam.endHUD();
  hint(ENABLE_DEPTH_TEST);