From our experience, we know that a link is usually some text in a paragraph. So a link element will be inside some <p> element. An image can be inside a paragraph of text, or can be independent and usually centered in a page.
Here are the tags of elements: <a> is the tag of link element, <img> is the tag of image element, and <center> is used to put some element in the center of page.
Here is an image showing what the structure of page can be like with link and images:
As you have seen, <img> cannot nest anything inside. So, like <br>, it does not need an end. In other words, there is no </img>.