centre align image in div
body {
margin: 0;
}
#over img {
margin-left: auto;
margin-right: auto;
display: block;
}Source: stackoverflow.com
position images in center of container
.image-container {
width: 500px;
height: 500px;
position: relative;
}
.image-container img {
position: absolute;
right: 0;
left: 0;
top: 0;
bottom: 0;
margin: auto auto;
}Source: stackoverflow.com