Similar to text generators, image generators produce images based on a natural language description. Also, like text generators, these AIs are trained on massive amounts of data, in this case images that also have textual descriptions.
Due to the large statistical representation of non-diverse images used to train such models, such generators have had issues with the way they produce images of humans when using non-specific prompts. E.g., Asking for the picture of a CEO and the image generated is of a white man.
Software such as Adobe and Canva have built-in AI assistants that can generate images or graphics for your project.