html/css hexagon with image inside

You can do it by overlaying corners like this:

http://jsfiddle.net/Eric/kGSCA/3/

HTML:

<div class="hexagon pic">
    <span class="top"></span>
    <span class="bottom"></span>
</div>

CSS:

.hexagon {
    background: url(http://placekitten.com/400/400/);
    width: 400px;
    height: 346px;
    position: relative;
}

.hexagon span {
    position: absolute;
    display: block;
    border-left: 100px solid red;
    border-right: 100px solid red;
    width: 200px;
}

.top {
    top: 0;
    border-bottom: 173px solid transparent;
}

.bottom {
    bottom: 0;
    border-top: 173px solid transparent;
}

The most flexible way of achieving a hexagon with an image is to use an inline SVG :

svg{
  width:30%;
}

<svg viewBox="0 0 100 100" version="1.1" xmlns="http://www.w3.org/2000/svg">
  <defs>
    <pattern id="img" patternUnits="userSpaceOnUse" width="100" height="100">
      <image xlink:href="https://farm9.staticflickr.com/8461/8048823381_0fbc2d8efb.jpg" x="-25" width="150" height="100" />
    </pattern>
  </defs>
  <polygon points="50 1 95 25 95 75 50 99 5 75 5 25" fill="url(#img)"/>
</svg>

There are at least two ways of achieving the hexagonal image with SVG :

• making an hexagonal polygon and filling the polygon with an image and the pattern element (approach I use in the previous snippet)
• clipping the image with an hexagonal polygon (see next snippet)

svg{width:30%}

<svg viewbox="0 0 100 100" version="1.1" xmlns="http://www.w3.org/2000/svg">
  <defs>
    <clipPath id="hexClip">
      <polygon points="50 1 99 25 99 75 50 99 1 75 1 25"/>
    </clipPath>
  </defs>  
  <image xlink:href="https://farm4.staticflickr.com/3165/5733278274_2626612c70.jpg" x="-25" width="150" height="100" clip-path="url(#hexClip)"/>
</svg>

The SVG approach allows control over many aspects of the hexagon shape and image. And they can be styled with CSS. Here is an example :

svg{
  width:30%;
  margin:0 auto;
}
#hex{
  stroke-width:2;
  stroke: teal;
  fill-opacity:0.6;
  transition:fill-opacity .8s;
}
svg:hover #hex {
  fill-opacity:1;
}
#text{
  stroke-width:0.5;
  stroke:teal;
  fill-opacity:0.4;
  fill:teal;
  transition:fill-opacity .8s;
}
svg:hover #text{
  fill-opacity:1;
}

<svg viewbox="0 0 100 100" version="1.1" xmlns="http://www.w3.org/2000/svg">
  <defs>
    <pattern id="img" patternUnits="userSpaceOnUse" width="100" height="100">
      <image xlink:href="https://farm9.staticflickr.com/8461/8048823381_0fbc2d8efb.jpg" x="-25" width="150" height="100" />
    </pattern>
  </defs>
  <polygon id="hex" points="50 1 95 25 95 75 50 99 5 75 5 25" fill="url(#img)"/>
  <text id="text" font-size="20" x="50" y="50" text-anchor="middle">Some text</text>
</svg>

For another approach to make hexagons with an image inside check this question : Responsive grid of hexagons

With CSS3 almost everything is possible: http://jsfiddle.net/kizu/bhGn4/

There I used different rotations with overflow: hidden, so you can get a cross-browser (well, modern cross-broser) masks that even can be coverable and clickable on the masked area.

A new and easy approach would be to use css3 clip-path property.

From Documentation:

The clip-path CSS property prevents a portion of an element from getting displayed by defining a clipping region to be displayed i.e, only a specific region of the element is displayed.

Following css will show a rectangular element in hexagon shape:

div.hexagon {
  clip-path: polygon(50% 0, 100% 25%, 100% 75%, 50% 100%, 0 75%, 0 25%);
}

Output Image:

body {
  background: linear-gradient(orange, yellow);
  min-height: 100vh;
  margin: 0;
}
.hexagon {
  clip-path: polygon(50% 0, 100% 25%, 100% 75%, 50% 100%, 0 75%, 0 25%);
  background: url("https://i.imgur.com/waDgcnc.jpg") no-repeat;
  background-size: cover;
  margin: 10px auto;
  height: 200px;
  width: 200px;      
}

<div class="hexagon">
  
</div>

We can use this property to draw any shapes that we want. Below are a couple of examples:

div.pentagon {
  clip-path: polygon(50% 0, 100% 45%, 80% 100%, 20% 100%, 0 45%);
}
div.octagon {
  clip-path: polygon(33.33% 0%, 66.66% 0%, 100% 33.33%, 100% 66.66%, 66.66% 100%, 33.33% 100%, 0 66.66%, 0 33.33%);
}

Output Image:

body {
  background: linear-gradient(orange, yellow);
  min-height: 100vh;
  margin: 0;
}
div {
  background: url("https://i.imgur.com/waDgcnc.jpg") no-repeat;
  background-size: cover;
  margin: 10px 20px;
  height: 170px;
  width: 170px;
  float: left;
}

.pentagon {
  clip-path: polygon(50% 0, 100% 45%, 80% 100%, 20% 100%, 0 45%);
}

.octagon {
  clip-path: polygon(33.33% 0%, 66.66% 0%, 100% 33.33%, 100% 66.66%, 66.66% 100%, 33.33% 100%, 0 66.66%, 0 33.33%);
}

<div class="pentagon">
  
</div>
<div class="octagon">
  
</div>

Note: clip-path css property is not supported in IE and Edge. However future versions of Edge are expected to have support for this property.