Both image and portrait refer to a means of showing how a person looks. In this sense both image and portrait means a photograph.
The traditional meaning of portrait is a photo taken about a person’s face sidewards while an image can be a photo taken about the person’s whole body. In literature, portrait is used also to describe characters.
Images can reflect not only persons but other object or landscape. Image can also mean opinion (for example, the public’s image of business meaning what the public thinks about business).
In summary, a portrait is a way to present what a person is like, while the image refers to showing anything is a visible form.
