function getImagePlaceholder(layer) {
  // get resources path
  let scriptPath = Context().scriptPath
  let rootDir = scriptPath
    .stringByAppendingPathComponent('/../../Resources/images/')
    .stringByStandardizingPath()

  // select placeholder size
  let placeholderImageFile = 'imagePlaceholder_'
  let maxDimension = Math.max(layer.frame().width(), layer.frame().height())
  if (maxDimension <= 220) {
    placeholderImageFile += 'small'
  } else if (maxDimension <= 416) {
    placeholderImageFile += 'medium'
  } else {
    placeholderImageFile += 'large'
  }

  return getImageData(`${placeholderImageFile}.png`, rootDir)
}
Creates image data representing the default image placeholder.

@param {MSLayer} layer
@return {MSImageData}