SOURCE

<div contenteditable=true>
  <p>
    <span class='checkbox checked'></span>span checkbox checked
  </p>
  <p>
    <span class='checkbox unchecked'></span>span checkbox checked
  </p>
  <p>
    <img class='checkbox selected' src='http://oj8dg2zpl.bkt.clouddn.com/2017/1525745632906.png'/>image checkbox
  </p>
</div>

.checkbox {
  display: inline-block;
  height: 24px;
  width:24px;
  vertical-align:middle;
  line-height:1;
}

.checked {
  background:url('http://oj8dg2zpl.bkt.clouddn.com/2017/1525745632906.png');
  background-repeat:no-repeat;
  background-position:center;
  background-size:cover;
}

.unchecked {
  background:url('http://oj8dg2zpl.bkt.clouddn.com/2017/1525746007194.png');
  background-repeat:no-repeat;
  background-position:center;
  background-size:cover;
}

img.selected {
  
}