Generates a mosaic of small tile images combined with a large main image

This functions goal generate a mosaic image based on a single (usually large) main
  image, and multiple small tile images. A large mosaic image will be randomly generated
  from the multiple tile images. The resulting mosaic image will be combined with the
  main image, forming the desired result. The ratio between images “strength” is defined
  by the Overlay Ratio ranging between [0:1]. Smaller value will make the large main
  image be dominant, while larger Overlay Ratio will make the mosaic image (formed from
  tiles images) more obvious, at the expense of the main image. The user can (and
  should) define regions with different Overlay Ratio values. For example when the main
  image is a portrait, the Overlay Ratio value around the face should be small (about
  0.2), while it can be high (about 0.7) in other less important areas. The user can
  also resize the final image, sharpen the small images, convert them to color (RGB) or
  Gray images, if needed.