看栈爆网这个问答:Unwanted padding-bottom of a div
方法一:
img { display:block; }
Since images are inline and text is inline, user agents leave some space for descender characters ( y, q, g ) also called line-height.
方法二:
img {vertical-align: bottom}
方法三:(假设img的父元素是.imgParent)
.imgParent {line-height: 0}
line-height 属性继承自其父元素,所以要在其父元素上设置这个值就可以了