Angular2: Show placeholder image if img src is not valid

The best way to handle broken image links is the use the onError event for the <img> tag:

<img  class="thumbnail-image" src="./app/assets/images/{{image.ID}}.jpg"
      onerror="this.src='./app/assets/images/placeholder.jpg';"  alt="..." />

<img [src]="pic" (error)="setDefaultPic()">

And somewhere in your component class:

setDefaultPic() {
  this.pic = "assets/images/my-image.png";
}