Image Resizing in PHP (Create Thumbnails Safely)

Uploading a 6MB image and showing it directly is a performance killer.
Professional apps generate thumbnails.

Common tools

• GD library (built-in in many PHP installs)
• Imagick (powerful if available)

Example (GD, JPEG to thumbnail)

<?php
$srcPath = __DIR__ . "/uploads/source.jpg";
$dstPath = __DIR__ . "/uploads/thumb.jpg";

$src = imagecreatefromjpeg($srcPath);

$srcW = imagesx($src);
$srcH = imagesy($src);

$thumbW = 300;
$thumbH = (int)($srcH * ($thumbW / $srcW));

$thumb = imagecreatetruecolor($thumbW, $thumbH);
imagecopyresampled($thumb, $src, 0, 0, 0, 0, $thumbW, $thumbH, $srcW, $srcH);

imagejpeg($thumb, $dstPath, 85);

imagedestroy($src);
imagedestroy($thumb);
?>

Why quality 85

Good balance between size and clarity.

Next: CSRF protection for APIs and cookies-based auth (advanced detail).