Call the function in your PHP and provide it with the variables:

$inputFIlename
and
$new_side

<?php

function resize_jpg($inputFilename, $new_side){
        $imagedata = getimagesize($inputFilename);
        $w = $imagedata[0];
        $h = $imagedata[1];

        if ($h > $w) {
                $new_w = ($new_side / $h) * $w;
                $new_h = $new_side;
        } else {
                $new_h = ($new_side / $w) * $h;
                $new_w = $new_side;
        }

        $im2 = ImageCreateTrueColor($new_w, $new_h);
        $image = ImageCreateFromJpeg($inputFilename);
        imagecopyResampled ($im2, $image, 0, 0, 0, 0, $new_w, $new_h, $imagedata[0], $imagedata[1]);
        return $im2;
}

?>

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