(PECL imagick 2, PECL imagick 3)
Imagick::flattenImages — Merges a sequence of images
This function has been DEPRECATED as of Imagick 3.4.4. Relying on this function is highly discouraged.
public Imagick::flattenImages ( ) : Imagick
Merges a sequence of images. This is useful for combining Photoshop layers into a single image.
 Returns true on success. 
Throws ImagickException on error.
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    https://www.php.net/manual/en/imagick.flattenimages.php