<div class="wrapper">
  <div class="header"></div>
    <div class="content">
      <img src="https://w.forfun.com/fetch/71/71f0c755f4b257fb9987c25743d16388.jpeg">
    </div>
    <div class="footer"></div>
</div>

.wrapper {
      min-height: 100%;
    display: block;  
height:auto;
}
.header {
  width:100%;
  height:100px;
  background:red;display: block;
}
.content {
  display: block;
  height:auto;
}
.content img{
width:auto;
max-width: 100%;
  height:auto;
  display: block;
}
.footer {
  width:100%;
  height:100px;display: block;
  background:green;