Q:

Place Image On White Background Using Imagick

Here is a GD version of what I intend to do. It places an image at the centre of a white background.
$background = imagecreatetruecolor(709,709);
$whiteBackground = imagecolorallocate($background, 255, 255, 255);
imagefill($background,0,0,$whiteBackground);
imagecopyresampled(
    $background, $new_img,(709-$imageWidth)/2,(709-$imageHeight)/2,
    0, 0, $imageWidth, $imageHeight, $width, $height
);
ImageJpeg ($background,"$path/$newName.$file_ext", 85);`

But I want it carried out using Imagick.

A:

Welcome to SO,
What you are looking for is flatten;
$im = new Imagick($old_img);
$im->setImageBackgroundColor('white');
$im->setImageAlphaChannel(11);
$im->mergeImageLayers(imagick::LAYERMETHOD_FLATTEN);
$im->setFormat("png");

$new = fopen($path . DIRECTORY_SEPARATOR . $newName . DIRECTORY_SEPARATOR . $file_ext, "w");
$im->writeImageFile($new);
$im->clear();
$im->destroy();

Not saying this is exactly what you are looking for, but it should help you well on your way.
the $im->setImageAlphaChannel(11); 
can be replaced by $im->setImageAlphaChannel(Imagick::ALPHACHANNEL_REMOVE); if your Imagic version is
3.2.0b2 or higher

