Agregar borde a PNG Outline CSS

img {
  -webkit-filter: drop-shadow(1px 1px 0 black)
                  drop-shadow(-1px -1px 0 black);
  filter: drop-shadow(1px 1px 0 black) 
          drop-shadow(-1px -1px 0 black);
}

body {
  background-color: lightcoral;
}
<img src="http://i.imgur.com/GZoXRjS.png" width="250">
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