div内的图像在图像下方有额外的空间

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>

解决方案

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>

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The included image is public domain and sourced from Wikimedia Commons