(PECL imagick 2.1.0)
Imagick::mergeImageLayers — Merges image layers
   Merges image layers into one. This method is useful when working with image
   formats that use multiple layers such as PSD. The merging is controlled using
   the layer_method which defines how the layers are merged.
   This method is available if Imagick has been compiled against ImageMagick version 6.3.7 or newer.
  
layer_method
       One of the Imagick::LAYERMETHOD_* constants
      
Returns an Imagick object containing the merged image.
Throws ImagickException on error.
Example #1 Imagick::mergeImageLayers()
<?php
function mergeImageLayers($layerMethodType, $imagePath1, $imagePath2) {
    $imagick = new \Imagick(realpath($imagePath));
    $imagick2 = new \Imagick(realpath($imagePath2));
    $imagick->addImage($imagick2);
    $imagick->setImageFormat('png');
    $result = $imagick->mergeImageLayers($layerMethodType);
    header("Content-Type: image/png");
    echo $result->getImageBlob();
}
?>