ref: https://stackoverflow.com/questions/13596794/resize-images-with-php-support-png-jpg

PHP Resize image - support jpge png gif.php

<?php
private function resize($newWidth, $targetFile, $originalFile) {

		$info = getimagesize($originalFile);
		$mime = $info['mime'];

		switch ($mime) {
		case 'image/jpeg':
			$image_create_func = 'imagecreatefromjpeg';
			$image_save_func = 'imagejpeg';
			$new_image_ext = 'jpg';
			break;

		case 'image/png':
			$image_create_func = 'imagecreatefrompng';
			$image_save_func = 'imagepng';
			$new_image_ext = 'png';
			break;

		case 'image/gif':
			$image_create_func = 'imagecreatefromgif';
			$image_save_func = 'imagegif';
			$new_image_ext = 'gif';
			break;

		default:
			throw new Exception('Unknown image type.');
		}

		$img = $image_create_func($originalFile);
		list($width, $height) = getimagesize($originalFile);

		$newHeight = ($height / $width) * $newWidth;
		$tmp = imagecreatetruecolor($newWidth, $newHeight);
		imagecopyresampled($tmp, $img, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);

		if (file_exists($targetFile)) {
			unlink($targetFile);
		}
		$image_save_func($tmp, "$targetFile.$new_image_ext");
	}