Align image in center and middle within div

I have following div

<div id="over" style="position:absolute; width:100%; height:100%>
 <img src="img.png">
</div>

How to align the image so as to be located in the middle and center of div ?


Solution 1:

body {
  margin: 0;
}

#over img {
  margin-left: auto;
  margin-right: auto;
  display: block;
}
<div id="over" style="position:absolute; width:100%; height:100%">
  <img src="http://www.garcard.com/images/garcard_symbol.png">
</div>

JSFiddle

Solution 2:

<div style="display:table-cell; vertical-align:middle; text-align:center">
<img src="img.png">
</div>

Solution 3:

This can also be done using the Flexbox layout:

STATIC SIZE

.parent {
    display: flex;
    height: 300px; /* Or whatever */
    background-color: #000;
}

.child {
    width: 100px;  /* Or whatever */
    height: 100px; /* Or whatever */
    margin: auto;  /* Magic! */
}
<div class="parent">
    <img class="child" src="https://i.vimeocdn.com/portrait/58832_300x300"/>
</div>

DYNAMIC SIZE

html, body {
  width: 100%;
  height: 100%;
  display: flex;
  background-color: #999;
}

* {
  margin: 0;
  padding: 0;
}

.parent {
  margin: auto;
  background-color: #000;
  display: flex;
  height: 80%;
  width: 80%;
}

.child {
  margin: auto;  /* Magic! */
  max-width: 100%;
  max-height: 100%;
}
<div class="parent">
  <img class="child" src="https://i.vimeocdn.com/portrait/58832_300x300"/>
</div>

I found the example in this article, which does a great job explaining the how to use layout.