You want to involve people in your advertising. So they pay attention to it, and maybe even tell other people about it.
Like so:
On Friday the 24th of February, in the heart of the Parisian business district La Défense, McDonald’s and BETC gave passers-by the opportunity to have their photo taken and integrated into the new McDonald’s outdoor print campaign.
From the looks of it, the participants had a good time. Which is the whole point of the McDonald’s brand experience. It’s a fun place with fun food. The brand’s advertising needs to reflect that, and in this case it does.