for_jeff.html

<script>
  window.onload = function (e) {
    var my_image = document.getElementById("image_id");             // Get a reference to the image tag
    var d = new Date();                                             // Instantiate a new date object
    
    if (d.getDay() == 3) {  // Sunday = 0, Monday = 1, etc...       // If today is Wednesday
      my_image.src = "path/to/other/image.png";                     // Change the image's src attribute
    }
  }
</script>