This is a close-in photograph of a sunflower with backlit petals. The only critical part of making this image was using as much of the field of focus as possible to get everything sharp. This image was photographed hand-held, if it wasn't for the wind a tripod would have helped.
The little flowers in the bigger flower head are call disc flowers. Each disc flower produces one seed. The colourful outer petals are called the ray flowers. Their purpose is to attract pollinators (e.g. bees) from a distance.