Trying to make an image opaque without affecting the border [duplicate]

Why in the following code the height of the div is bigger than the height of the img ? There is a gap below the image, but it doesn't seems to be a padding/margin.

What is the gap or extra space below image?

#wrapper {
  border: 1px solid red;
  width:200px;
}
img {
  width:200px;
}

<div id="wrapper">
  <img src="http://i.imgur.com/RECDV24.jpg" />
</div>

Solution 1:

By default, an image is rendered inline, like a letter so it sits on the same line that a, b, c and d sit on.

There is space below that line for the descenders you find on letters like g, j, p and q.

You can:

• adjust the vertical-align of the image to position it elsewhere (e.g. the middle) or
• change the display so it isn't inline.

div {
  border: solid black 1px;
  margin-bottom: 10px;
}

#align-middle img {
  vertical-align: middle;
}

#align-base img {
  vertical-align: bottom;
}

#display img {
  display: block;
}

<div id="default">
<h1>Default</h1>
  The quick brown fox jumps over the lazy dog <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/VangoghStarry-night2.jpg/300px-VangoghStarry-night2.jpg" alt="">
</div>

<div id="align-middle">
<h1>vertical-align: middle</h1>
  The quick brown fox jumps over the lazy dog <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/VangoghStarry-night2.jpg/300px-VangoghStarry-night2.jpg" alt=""> </div>
  
  <div id="align-base">
<h1>vertical-align: bottom</h1>
  The quick brown fox jumps over the lazy dog <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/VangoghStarry-night2.jpg/300px-VangoghStarry-night2.jpg" alt=""> </div>

<div id="display">
<h1>display: block</h1>
  The quick brown fox jumps over the lazy dog <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/VangoghStarry-night2.jpg/300px-VangoghStarry-night2.jpg" alt="">
</div>

The included image is public domain and sourced from Wikimedia Commons

Solution 2:

Another option suggested in this blog post is setting the style of the image as style="display: block;"

Solution 3:

Quick fix:

To remove the gap under the image, you can:

• Set the vertical-align property of the image to vertical-align: bottom; vertical-align: top; or vertical-align: middle;
• Set the display property of the image to display:block;

See the following code for a live demo:

#vAlign img {
  vertical-align :bottom;
}
#block img{
  display:block;
}

div {border: 1px solid red;width:100px;}
img {width:100px;}

<p>No fix:</p>
<div><img src="http://i.imgur.com/RECDV24.jpg" /></div>

<p>With vertical-align:bottom; on image:</p>
<div id="vAlign"><img src="http://i.imgur.com/RECDV24.jpg" /></div>

<p>With display:block; on image:</p>
<div id="block"><img src="http://i.imgur.com/RECDV24.jpg" /></div>

Explanation: why is there a gap under the image?

The gap or extra space under the image isn't a bug or issue, it is the default behaviour. The root cause is that images are replaced elements (see MDN replaced elements). This allows them to "act like image" and have their own intrinsic dimensions, aspect ratio....
Browsers compute their display property to inline but they give them a special behaviour which makes them closer to inline-block elements (as you can vertical align them, give them a height, top/bottom margin and padding, transforms ...).

This also means that:

<img> has no baseline, so when images are used in an inline formatting context with vertical-align: baseline, the bottom of the image will be placed on the text baseline.
(source: MDN, emphasis mine)

As browsers by default compute the vertical-align property to baseline, this is the default behaviour. The following image shows where the baseline is located on text:

(Image source)

Baseline aligned elements need to keep space for the descenders that extend below the baseline (like j, p, g ...) as you can see in the above image. In this configuration, the bottom of the image is aligned on the baseline as you can see in this example:

div{border:1px solid red;font-size:30px;}
img{width:100px;height:auto;}

<div>
  <img src="http://i.imgur.com/RECDV24.jpg" />jpq are letters with descender
</div>

This is why the default behaviour of the <img> tag creates a gap at the bottom of it's container and why changing the vertical-align property or the display property removes it as in the following demo:

div {width: 100px;border: 1px solid red;}
img {width: 100px;height: auto;}

.block img{
  display:block;
}
.bottom img{
  vertical-align:bottom;
}

<p>Default:</p>
<div>
  <img src="http://i.imgur.com/RECDV24.jpg" />
</div>
<p>With display:block;</p>
<div class="block">
  <img src="http://i.imgur.com/RECDV24.jpg" />
</div>
<p>With vertical-align:bottom;</p>
<div class="bottom">
  <img src="http://i.imgur.com/RECDV24.jpg" />
</div>