Why doesn't the library work with Imagick? How to fix it?

I have such code:

require_once 'vendor/autoload.php';
$imagePath = __DIR__ . '/photo.jpg';
$thumb = new phpThumb();
$thumb->setSourceFilename($imagePath);
$thumb->setParameter('w', 100);
$thumb->setParameter('h', 100);
if ($thumb->GenerateThumbnail()) {
    $thumb->OutputThumbnail();
}

As a result of his work, I get a white picture with black letters "no GD":

I don't really have GD, but I do have Imagick. The README says that the library also works with Imagick:

phpThumb() uses the GD library and/or ImageMagick to create thumbnails from images

I decided to check if Imagick works. I wrote this code:

$sourceImagePath = __DIR__ . '/photo.jpg';
$image = new Imagick($sourceImagePath);
$newWidth = 100;
$newHeight = 100;
$image->resizeImage($newWidth, $newHeight, Imagick::FILTER_LANCZOS, 1);
$destinationImagePath =  __DIR__ . '/photoRes.jpg';
$image->writeImage($destinationImagePath);
$image->clear();
$image->destroy();
echo 'Success!';

I got "Success" and a processed file called photoRes.jpg appeared in the folder. That is, Imagick works. Why is phpThumb not working then? How to fix it?

JamesHeinrich / phpThumb

Why doesn't the library work with Imagick? How to fix it? #217