Coming from a computer vision perspective my motivation here is that most mosaics that tile images try to match only the color of the image for each specific location but they do not capture other characteristics like gradients (a sense of directionality) which is a common feature in most of today's computer vision systems. Take as inspiration the picture of the Starry Night by Vincent Van Gogh, made available by the Google Art Project at incredible resolutions. I'm including here a pretty high res picture if you click on it but feel free to explore the link above.
|Click on the image for higher resolution.|
|Click on the image for higher resolution|