Send string to php gd through ajax request

Question

I try to create a captcha code image with php gd :

$im = imagecreatetruecolor(100, 25);
$white = imagecolorallocate($im, 255, 255, 255);
$black = imagecolorallocate($im, 0, 0, 0);
imagefilledrectangle($im, 0, 0, 399, 29, $white);
$imgstring=$_GET['captcha'];
$font = 'RAVIE.TTF';
imagettftext($im, 15, 0, 10, 20, $black, $font, $imgstring);
header('Content-Type: image/png');
imagepng($im);
imagedestroy($im);

The GET value is send with ajax like this:

var randstring;
function Captcha() {
    randstring = Math.round((Math.pow(36, length + 1) - Math.random() * Math.pow(36, 5))).toString(36).slice(1);

            $.ajax({
                url: 'test_image.php',
                data: {'captcha' : randstring},
                method: 'GET',
                success: function (data){
                    console.log(data);
                },
                error: function (){
                    alert('Error');
                    return false;
                }   

            });
        }

HTML:

<img src="test_image.php">

Though it gives no errors , the image is not generated . Yes, the request reach the php script , i already checked , but something blocks image from being generated...

UPDATE Actually the image is generated, and also the ajax request is sent. But on the test_image.php script , $_GET['captcha'] ( the request ) is not recognized so it will just output a blank string in that image , though the image is there , but without a string .

Answer 1

You want to load the content of your image using AJAX but do not want to put URL in img tag for security reason. So, in that case, you should fetch base64 encoded data of the image and use it inside your img src.

Use following code for your php file:

<?php

// Start output buffering
ob_start();
$im = imagecreatetruecolor(100, 25);
$white = imagecolorallocate($im, 255, 255, 255);
$black = imagecolorallocate($im, 0, 0, 0);
imagefilledrectangle($im, 0, 0, 399, 29, $white);
$imgstring=$_GET['captcha'];
$font = 'RAVIE.TTF';
imagettftext($im, 15, 0, 10, 20, $black, $font, $imgstring);
imagepng($im);
imagedestroy($im);

// Get Image content a variable
$captchaImageData=ob_get_contents();
// Clean the output buffer
ob_end_clean();

//Base64 Encode
$encodedData = base64_encode($captchaImageData);

echo $encodedData;
?>

You Javascript code will be following:

function Captcha() {
    var randstring = Math.round((Math.pow(36, length + 1) - Math.random() * Math.pow(36, 5))).toString(36).slice(1);

    $.ajax({
        url: 'test_image.php',
        data: {'captcha' : randstring},
        method: 'GET',
        beforeSend: function(data) {
            $('captchaImage').attr('src','laoding.gif');
        },
        success: function (data){
            // data is base64_encoded data of your image
            // load it in your img suorce
            $('captchaImage').attr('src','data:image/png;base64,'+data);
        },
        error: function (){
            alert('Error');
            $('captchaImage').attr('src','error.jpg');
        }   

    });
}

You HTML element will be updated with an ID. Also put some sort of loading gif/animation until image is loaded.

<img src="loading.gif" id="captchaImage">

Now calling Captcha() funciton in javascript will always load a new captcha image. Put appropriate loading.gif and error.jpg images