How can images be resized using Bootstrap

Just add this somewhere in your stylesheet and it will apply to all images on your site.

img {
  display: block;
  max-width: 100%;
  height: auto;
}

Bootstrap v3 and below.

Use class="img-responsive" in the image tag. This will automatically adjust the size based on the screen size. Its a bootstrap class.

Ex: http://www.w3schools.com/bootstrap/tryit.asp?filename=trybs_img_responsive&stacked=h

Bootstrap v4

Use class="img-fluid" in the image tag. This will automatically adjust the size based on the screen size. Its a bootstrap class. see comment below for more details