Insert below code in your website

<div id="FixedPositionWrapper">
    <div id="FixedPositionOuter">
        <div id="FixedPositionInner">
            <a href="#"><img src="images/image.jpg"></a>
        </div>
    </div>
</div>

Insert below line in your css file

#FixedPositionWrapper {
  margin: auto;
  position: fixed;
  margin: auto;
  right: 0;
  bottom: 0;
  z-index:99999;
}
#FixedPositionOuter {
  width: 100%;
}
#FixedPositionInner {
  font-size: 18pt;
  font-family: Tahoma;
  text-align: right;
  color: white;
  margin-bottom: 150px;
} 

@media only screen and (max-width : 768px){
#FixedPositionWrapper {
  display: none;
}
}