onchange file input change img src and change image color

onchange event is not working. What am I supposed to do to get result on same page. I dont want to redirect to any other page to upload image. Is this issue is because of opencart? I dont know if it is correct to write like this in cpanel. I am using opencart and cpanel. Is there any other way?

HTML

 <input type='file' id="upload" onchange="readURL(this.value)" />
    <img id="img" src="#" alt="your image" />

script

function readURL(input) {
var url = input.value;
var ext = url.substring(url.lastIndexOf('.') + 1).toLowerCase();
if (input.files && input.files[0]&& (ext == "gif" || ext == "png" || ext == "jpeg" || ext == "jpg")) {
    var reader = new FileReader();

    reader.onload = function (e) {
        $('#img').attr('src', e.target.result);
    }
    reader.readAsDataURL(input.files[0]);
}
else{
     $('#img').attr('src', '/assets/no_preview.png');
  }
}

JSFiddle

You need to send this object only instead of this.value while calling onchange

<input type='file' id="upload" onchange="readURL(this)" />

because you are using input variable as this in your function, like at line

var url = input.value;// reading value property of input element

Working DEMO

EDIT - Try using jQuery like below --

remove onchange from input field :

<input type='file' id="upload" >

Bind onchange event to input field :

$(function(){
  $('#upload').change(function(){
    var input = this;
    var url = $(this).val();
    var ext = url.substring(url.lastIndexOf('.') + 1).toLowerCase();
    if (input.files && input.files[0]&& (ext == "gif" || ext == "png" || ext == "jpeg" || ext == "jpg")) 
     {
        var reader = new FileReader();

        reader.onload = function (e) {
           $('#img').attr('src', e.target.result);
        }
       reader.readAsDataURL(input.files[0]);
    }
    else
    {
      $('#img').attr('src', '/assets/no_preview.png');
    }
  });

});

jQuery Demo

Simple Solution. No Jquery

<img id="output" src="" width="100" height="100">

<input name="photo" type="file" accept="image/*" onchange="document.getElementById('output').src = window.URL.createObjectURL(this.files[0])">

in your HTML : <input type="file" id="yourFile"> don't forget to reference your js file or put the following script between <script></script> in your script :

var fileToRead = document.getElementById("yourFile");

fileToRead.addEventListener("change", function(event) {
  	var files = fileToRead.files;
   	if (files.length) {
   		console.log("Filename: " + files[0].name);
   		console.log("Type: " + files[0].type);
   		console.log("Size: " + files[0].size + " bytes");
   	}
       
}, false);

Try with this code, you will get the image preview while uploading

<input type='file' id="upload" onChange="readURL(this);"/>
<img id="img" src="#" alt="your image" />

 function readURL(input){
 var ext = input.files[0]['name'].substring(input.files[0]['name'].lastIndexOf('.') + 1).toLowerCase();
if (input.files && input.files[0] && (ext == "gif" || ext == "png" || ext == "jpeg" || ext == "jpg")) 
    var reader = new FileReader();
    reader.onload = function (e) {
        $('#img').attr('src', e.target.result);
    }

    reader.readAsDataURL(input.files[0]);
}else{
     $('#img').attr('src', '/assets/no_preview.png');
}
}

Below solution tested and its working, hope it will support in your project.
HTML code:
    <input type="file" name="asgnmnt_file" id="asgnmnt_file" class="span8" 
    style="display:none;" onchange="fileSelected(this)">
    <br><br>
    <img id="asgnmnt_file_img" src="uploads/assignments/abc.jpg" width="150" height="150" 
    onclick="passFileUrl()" style="cursor:pointer;">

JavaScript code:
    function passFileUrl(){
    document.getElementById('asgnmnt_file').click();
    }

    function fileSelected(inputData){
    document.getElementById('asgnmnt_file_img').src = window.URL.createObjectURL(inputData.files[0])
    }