如何使用imagemagick创建水印

I'm trying to create a watermark with ImageMagick however, the guides on layering are pretty daunting. Basically I'll have one base image say "base.jgp" and an overlay image say "overlay.jpg". Overlay.jpg would be smaller than base.jpg. Which exec command would I run to place overlay centered on top of base.jpg?

Thanks!

shell_exec("composite -gravity center ./images/watermark_horizontal.png {$this->path} {$this->path}");

Here we go

Check out ImageMagick examples, especially the Compositing Images chapter. It has a number of ready-made real-world examples.

$image = new Imagick();
$image->readImage("image.jpg");

// Open the watermark
$watermark = new Imagick();
$watermark->readImage("watermark.png");

// Overlay the watermark on the original image
$image->compositeImage($watermark, imagick::COMPOSITE_OVER, 0, 0);

// send the result to the browser
header("Content-Type: image/" . $image->getImageFormat());