Pretty cool! I think the API docs could possibly be a bit more precise, though. Perhaps something like this:

  You can also pass us the following optional query parameters.
  Parameter 	Default 	Description
  size 		128 	 	integer	Image size: Length of longest side, in pixels
  format 	"png"	 	string	File format, either "png" or "jpg"
  greyscale 	(not passed) 	boolean	If this parameter is passed, image will be desaturated