Resize image in PHP

You need to use either PHP's ImageMagick or GD functions to work with images.

With GD, for example, it's as simple as...

function resize_image($file, $w, $h, $crop=FALSE) {
    list($width, $height) = getimagesize($file);
    $r = $width / $height;
    if ($crop) {
        if ($width > $height) {
            $width = ceil($width-($width*abs($r-$w/$h)));
        } else {
            $height = ceil($height-($height*abs($r-$w/$h)));
        }
        $newwidth = $w;
        $newheight = $h;
    } else {
        if ($w/$h > $r) {
            $newwidth = $h*$r;
            $newheight = $h;
        } else {
            $newheight = $w/$r;
            $newwidth = $w;
        }
    }
    $src = imagecreatefromjpeg($file);
    $dst = imagecreatetruecolor($newwidth, $newheight);
    imagecopyresampled($dst, $src, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);

    return $dst;
}

And you could call this function, like so...

$img = resize_image(‘/path/to/some/image.jpg’, 200, 200);

From personal experience, GD's image resampling does dramatically reduce file size too, especially when resampling raw digital camera images.

Simply use PHP's GD functions (like imagescale):

Syntax:

imagescale ( $image , $new_width , $new_height )

Example:

Step: 1 Read the file

$image_name =  'path_of_Image/Name_of_Image.jpg|png|gif';      

Step: 2: Load the Image File

 $image = imagecreatefromjpeg($image_name); // For JPEG
//or
 $image = imagecreatefrompng($image_name);   // For PNG
 //or
 $image = imagecreatefromgif($image_name);   // For GIF

Step: 3: Our Life-saver comes in '_' | Scale the image

   $imgResized = imagescale($image , 500, 400); // width=500 and height = 400
//  $imgResized is our final product

Note: imagescale will work for (PHP 5 >= 5.5.0, PHP 7)

Step: 4: Save the Resized image to your desired directory.

imagejpeg($imgResized, 'path_of_Image/Name_of_Image_resized.jpg'); //for jpeg
imagepng($imgResized, 'path_of_Image/Name_of_Image_resized.png'); //for png

Source : Click to Read more