In order for the images to auto fit to slider containers use width 100% on <img>. Check CSS below
$(document).ready(function() {
$("#owl-demo").owlCarousel({
autoPlay: 3000, //Set AutoPlay to 3 seconds
items : 4,
itemsDesktop : [1199,3],
itemsDesktopSmall : [979,3]
});
});
<div id="owl-demo">
<div class="item"><img src="assets/owl1.jpg" alt="Owl Image"></div>
<div class="item"><img src="assets/owl2.jpg" alt="Owl Image"></div>
<div class="item"><img src="assets/owl3.jpg" alt="Owl Image"></div>
<div class="item"><img src="assets/owl4.jpg" alt="Owl Image"></div>
<div class="item"><img src="assets/owl5.jpg" alt="Owl Image"></div>
<div class="item"><img src="assets/owl6.jpg" alt="Owl Image"></div>
<div class="item"><img src="assets/owl7.jpg" alt="Owl Image"></div>
<div class="item"><img src="assets/owl8.jpg" alt="Owl Image"></div>
</div>
#owl-demo .item{
margin: 3px;
}
#owl-demo .item img{
display: block;
width: 100%;
height: auto;
}