const img = document.getElementById('preview');
const input = document.getElementById('picker');
input.onchange = function(ev) {
  const file = ev.target.files[0]; // get the file
  const blobURL = URL.createObjectURL(file);
  img.src = blobURL;
}

<div class="container">
  <input type="file" class="title3" id="picker" />
  <img id="preview" alt="IDK why, but I can't display that." class="title3" width="200">
</div>

const selectFile = evt => {
  const [file] = evt.target.files;
  if (file) {
    document.getElementById('preview').src = URL.createObjectURL(file);
  }
}

<div class="container">
  <input type="file" class="title3" id="picker" onchange="selectFile(event)" />
  <img id="preview" alt="IDK why, but I can't display that." class="image">;
</div>

 <div class="container">
        <input type="file" class="title3" id="picker"/>
        <img src= this.input alt="IDK why, but I can't display that." class="title3">;