Image converting in PHP - php

Question

I have a book where is a sample for creating a whole new picture, from a random picture given by the user, and I think there is something wrong in the example, at least I can't use it. The error code gave back by the PHP in the browser:
Fatal error: Uncaught Error: Call to undefined function imagecreatefromstring() in C:\xampp\htdocs\kepkonvertalas.php:13 Stack trace: #0 {main} thrown in C:\xampp\htdocs\kepkonvertalas.php on line 13
The HTML form:
<form action="kepkonvertalas.php" method="post" enctype="multipart/form-data">
<input type="file" name="kep"><br>
<input type="submit" value="kuldes">
</form>
The PHP part:
<?php
$fajl = $_FILES['kep']['tmp_name'];
$kep = file_get_contents($fajl);
$forraskep = imagecreatefromstring($kep);
$szelesseg = imageSX($forraskep);
$magassag = imageSY($forraskep);
$ujmagassag = 400;
$ujszelesseg = $ujmagassag*($szelesseg/$magassag);
$ujkep = imagecreatetruecolor($ujszelesseg, $ujmagassag);
$eredmeny = imagecopyresampled($ujkep, $forraskep, 0, 0, 0, 0, $ujszelesseg, $ujmagassag, $szelesseg, $magassag);
imagejpeg($ujkep, "ujkep.jpg");
?>
<img src="ujkep.jpg" alt="">`
What is suspect, is that this extension is not implemented into my php.ini, but I cant find any proof for it, either solve the problem. Thanks for the help!
I tried to implement a picture from an URL, and do the conversion on that, which means I deleted the
$fajl = $_FILES['kep']['tmp_name'];
$kep = file_get_contents($fajl);`
And I've made a variable with a picture URL, and in the
$forraskep = imagecreatefromstring($kep);
I just changed like this:
$forraskep = imagecreatefromstring(file_get_contents($src);
Well the next problem was, that the $forraskep variable was not defined.
I expect an output where I have the picture with the size of the given parameters.

Answer 1

The solution was actually kinda easy:
open php.ini
search for "extension=gd"
delete the semicolon
restart apache server