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function previewImg(event) {
  if (event.target.files && event.target.files[0]) {
    var reader = new FileReader();

    reader.onload = function (e) {
      $('#img-input-file-preview').attr('src', e.target.result);
    };

    reader.readAsDataURL(event.target.files[0]);
  }
}

$("#img-input-file").on('change', previewImg);

<form id="my_form">
  <input type="file" id="img-input-file">
  <img id="#img-input-file-preview" src="#" alt="imagen" />
</form>