The DPP make decisions about how likely a prosecution is to suceed. The fact that there was no prosecution only proves that the DPP could not commit to that particular case. That is a far cry from exonerating the poster. The fact that racist hate crimes increased sharply following the referendum indicates that there was a link between the racist nature of some of the leave propaganda, including that poster, and motivation for such crimes.

There could be other reasons for the increase in hate crimes of course but, to date, no one has yet out any forward.