- type: (string) Determines the style for the composition.
'plain' or 'polaroid' are supported.
- resize_height: (integer) The height that each individual thumbnail
should be resized to before composing on the image.
- padding: (integer) How much padding should we ensure is left around
the active image area?
- background: (string) The background canvas color - this is used as
the color to set any padding to.
- bordercolor: (string) If using type 'plain' this sets the color of
the border that each individual thumbnail gets.
- borderwidth: (integer) If using type 'plain' this sets the width of
the border on each individual thumbnail.
- offset: (integer) If using type 'plain' this determines the amount
of x and y offset to give each successive image when it is
placed on the top of the stack.