Check out example codes for "file upload preview in html". It will help you in understanding the concepts better.

Code Example 1

<html>
<head>
<script type='text/javascript'>
function preview_image(event) 
{
 var reader = new FileReader();
 reader.onload = function()
 {
  var output = document.getElementById('output_image');
  output.src = reader.result;
 }
 reader.readAsDataURL(event.target.files[0]);
}
</script>
<style>
body
{
 width:100%;
 margin:0 auto;
 padding:0px;
 font-family:helvetica;
 background-color:#0B3861;
}
#wrapper
{
 text-align:center;
 margin:0 auto;
 padding:0px;
 width:995px;
}
#output_image
{
 max-width:300px;
}
</style>
</head>
<body>
<div id="wrapper">
 <input type="file" accept="image/*" onchange="preview_image(event)">
 <img id="output_image"/>
</div>
</body>
</html>

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