Not every image that is used in advertising has a functional objective. Take fashion ads, for example, sometimes the product is missing all together.
- Images that show something highly specific: a product, a medical condition, a location
- Images that show a relevant scene or background: people tapping on their mobile phone, a driver in a traffic jam, calm bamboo forest, a sunset
- Images that make a visual metaphor: a prisoner in a cage, a cat chasing a mouse
- Images that just set the mood of the presentation
I use 1. and 4. more, and 2. and 3. less because they often lead to visual cliches.
Art: "Self-Portrait, Yawning" by Joseph Ducreux, 1783