A key visual is the single hero image a campaign is built around, designed so that every other asset in the campaign can be adapted from it and still look like the same idea.
The test is not whether it is beautiful. It is whether it survives being cropped to a square, a vertical story, a billboard, and a 320-pixel banner while remaining recognizably the same campaign.
What makes one work
A single focal idea. One thing happening. Key visuals that contain two ideas become two campaigns the moment they are cropped.
Composition that tolerates reframing. Space where text will go, a subject that does not sit dead center, and nothing critical near the edges. Most key visuals fail here first.
Legibility at thumbnail size. If the idea disappears at 200 pixels wide it will not work in a feed, which is where most of the impressions are.
A palette the rest of the campaign can inherit. The key visual sets the color story that every adaptation reuses.
Key visual vs style frame vs hero shot
A style frame proves how the work will look; it is an internal tool. A key visual is the campaign's actual centerpiece, produced to ship. A hero shot is the product presented at its best, which may or may not be the key visual, depending on whether the campaign idea is the product or something around it.
How many you need
One per campaign, adapted. Teams that produce five key visuals have produced five campaigns, and the media budget will only fund one of them properly.
The exception is a campaign running across genuinely different audiences, where one idea might need two executions. Even then, the adaptations should share the palette, the typography, and the compositional logic, or the campaign reads as unrelated ads.
Examples
A beverage launch. The can mid-pour against deep shadow, positioned right of frame with the left two thirds open for the line. Crops to vertical by tightening on the pour, crops to square by losing the shadow, works at thumbnail because the silhouette reads.
A software brand. An illustrated system diagram with one element highlighted, built on a grid so any crop still contains the highlight. The adaptation logic was decided before the illustration was made, which is why it worked.
Related concepts
What is a hero shot covers the product-first variant. Multi-format export workflow covers adapting one visual into a full format set. What is a brand board covers the identity rules a key visual has to obey.
The efficient way to build one: generate the key visual, then generate its crops from the same source on the same canvas so the adaptations never drift from the original. The 8frame canvas is free and unlimited, and generation is paid from $19/month.