In earlier versions of Kirby images were by default renamed to begin with a project sorting number. This made Kirby an impossible sell for my clients whos businesses depend at least in some part on organic search traffic. Does Kirby 3 still apply these numbers to URLs?
No, Kirby 3 stores files in a separate media folder without the sorting numbers.
Even in Kirby 2 is was possible to get rid of the folder sorting numbers, though.