How to center image in carousel

You've got two options

1. If you want the image to take up entire carousel then

img 
{
   width: 100%;
   height: auto;
}

2. If you dont want the image to stretch 100 %, then set your desired width(or dont, just specify margin) and margin auto:

img
{
   width: 50%;
   margin: auto;
}

I know I am super late but in case that someone is searching for an answer today I just found out that for me the best solution was to put the image in a separate div in the .carousel-item and then center it using flex:

<div class="carousel-item">
    <div class="d-flex justify-content-center">
        <img src="img.png" alt="img.png">
    </div>
</div>