An image is a picture shown on a page. It can help someone recognize a product, understand an idea, or remember what a person looks like. Think of a photo in a guidebook: it adds a visual clue alongside the words.
For example, a recipe page might show what the finished dish looks like. A picture should support the page's purpose rather than decorate it without adding meaning.
If the image communicates something important, provide a short description for people who cannot see it. If it is only decoration, it should not distract from the page's actual information.