Some capitals such as New York, London or paris, are covered with a beautiful and quite hyper resistant street art project called "Invasion", made by... "Invader". This consit in reproducing pixel-drawings (also named as "sprites" in the video game industry) with mosaic and stick it on the walls, in the streets. invader has a simple technique : he is using a glue that is more solid and resistant than the tiles itself, so any attempt to steal these pieces of street art remain unsuccessful. Quite clever!
Knowing nothing about how to do tiles mosaic and where to by the stuff, I started to do some searchs on google image to find an appropriate drawing to convert into mosaic. With a bit of luck I knew I could find one that will exactly fit my wills : not too small, and not to large. A 25x25 tiles mosaic was my absolute limit as it's already involving 625 tiles.
I finally failed in google images, and before starting to convert a bigger image into a smaller one, I did some extra effort to find an original sprite with the size I wanted (pixel design is so well done that I couldn't expect to get the same quality by myself). I finally found the exact 18x18 pixels image I wanted, in a backup of a nintendo GameBoy Advance cartrige. I had to extract the content and one particular design on a splash screen fitted my needs perfectly. I can't reproduce the drawing here as it's strongly under copyright.