<ul class="selectables">
  <label>
    <input type="checkbox">
    <img src="//dummyimage.com/100x100">
  </label>
  <label>
    <input type="checkbox">
    <img src="//dummyimage.com/100x100">
  </label>
  <label>
    <input type="checkbox">
    <img src="//dummyimage.com/100x100">
  </label>
</ul>

ul.selectables li {
  display:inline-block;
}
 
ul.selectables input {
  display:none;
}
 
ul.selectables input:checked + img {
  outline:solid 2px red;
}