image validation

html form
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<form onsubmit="return false"  class="form-horizontal" name="ads_post" id="post_form" enctype="multipart/form-data" method="post">
<div class="form-group">
      <label class="control-label col-sm-2" >Image</label>
      <div class="col-sm-10">
      <table>
        <tr>
        <td><input type="file"  class="file" name="file" id="input-upload-img1"></td>

        </tr>
     </table>
      </div>
      <span class="img_error"></span>
    </div>
<div class="form-group">
                      <div class="col-sm-offset-2 col-sm-10">
                        <button type="submit" class="btn btn-primary" name="ad_submit">Submit</button>
                      </div>
                    </div>
</form>

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validate.js
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$(document).ready(function(){

   function verify_img(img){

    $(".img_error").hide();
    if(img == ""){
    $(".img_error").show();
    $(".img_error").html("plz Choose an image");
    return false;
    }
    else{
    $(".img_error").show();
    $(".img_error").html("validating....");
    $.ajax({

            url:"classes/process.php",
            type: "POST",
            data: {check_img:1,img:img},
            success: function(data)
            {

    alert(data);

    },error: function(req, status, error) {
          // alert('Error: ' + req.status);
            console.log(error);
            console.log();
            }

     })
    }

}


$("#input-upload-img1").focusout(function(){
        var img=$("#input-upload-img1").val();
        verify_img(img);

          })



})


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process.php
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<?php

include "dbcon.php";

class DataOperation extends database{



public function verify_img($file){

    $regexp ="/\.(jpe?g|png)$/i";
    return (!preg_match($regexp,$title)) ? "Invalid_extension" : 'ok';

    }

}

$obj = new DataOperation;

if(isset($_FILES['file']['check_img'])){
     $file=$_FILES['file']['img'];
     echo $data=$obj->verify_img($file);
     exit();
 }


 ?>