<div>
  <div>Image1</div>
  <div>Image2</div>
  <div>Image3</div>
</div>

<div>
  <div>Image1</div>
  <div>Image2</div>
</div>

<div>
 <div>Image1</div>
 <div>Image2</div>
</div>

<div>
 <div>Image3</div>
 <div>Image4</div>
</div>

.hideme { display: none; }

<div>
  <div>Image1</div>
  <div>Image2</div>
  <div class="hideme">Image3</div>
</div>

div:nth-child(3) {
    display:none;
}

<div>
  <div>Image1</div>
  <div>Image2</div>
  <div class="ThingTohide">Image3</div>
</div>

@media only screen and (min-width:300px) and (max-width:480px) {
    .ThingTohide {
        display: none;
    }
}

<div>
 <div>Image1</div>
 <div>Image2</div>
 <div class="move">Image3</div>
</div>

<div class="group2">
 <div>Image4</div>
</div>

$(document).ready(function(){
    if ($(window).width()<640) { //to check if it's on mobile device, or any other method if it's not suits you
        $('.move').prependTo('.group2');
    };
});