class Magick::ImageList

def is_an_image_array(ary)

Ensure array is always an array of Magick::Image objects 
def is_an_image_array(ary)
    unless ary.respond_to? :each
        Kernel.raise ArgumentError, "Magick::ImageList or array of Magick::Images required (#{ary.class} given)"
    end
    ary.each { |obj| is_an_image obj }
    true
end