Most people see a campaign while moving: on a bus, crossing a road, scrolling a feed. Designing for that movement changes how an image should be built.
One read, two seconds
An outdoor image has about two seconds to register. Strong silhouettes, a dominant colour and a single focal point survive that test better than detail.
Sequences, not single images
In cities, people encounter the same campaign several times in different places. I plan images as a sequence, so each new encounter adds something instead of repeating.
The city becomes the layout, and the campaign is read over days rather than seconds.