Why doesn't the logo appear in the navbar?

Question

HTML

<!--- Navigation -->
<nav class = "navbar navbar-expand-md navbar-dark bg-dark fixed-top">
  <a class = "navbar-brand" href = "#"><img src = "img/nuno.jpg"></a>
</nav>
<!--- End Navigation -->

Instead of a picture, this appears:

Answer 1

gaps in the code, wrong graphics format