how to change image src jquery code example

Example 1: jquery change picture source

$("#my_image").attr("src","second.jpg");

Example 2: jquery change picture source

// https://codepen.io/kman/pen/dXjpoX
// Stockphotos JS

$(document).ready(function(){
  var flag = 0;  
  $("button#changeSize").click(function(){
    if(flag == 0) {
      $("#dummyimage").attr("src","http://dummyimage.com/350x155/");
      flag = 1;
    }
    else if(flag == 1) {
      $("#dummyimage").attr("src","http://dummyimage.com/450x255/");
      flag = 0;
    }
  });
});