--------hr--------
 text

--------hr--------
[           ]
[   image   ]
[           ]
text

<div class="thumbnail">
<img src="myimage.jpeg" />
<div class="caption">caption</div>
</div>
img { width: 100% }

<div class="placeholder">
    <div class="myimage" style="background-image: url({somedynamicimageurl})"><img /></div>
</div>

.placeholder {
    width: 300;
    height: 300;
    background-repeat: no-repeat;
    background-size: contain;
    background-image: url('my_placeholder.png');
}