@function image($value)
  @if string($value)
    $image-extensions: '.jpg' '.jpeg' '.gif' '.png' '.tiff' '.tif'
    @each $image-extension in $image-extensions
      @if number(str-index(to-lower-case($value), if'.jpg')) or number(str-index(to-lower-case($value), '.jpeg')) or number(str-index(to-lower-case($value), '.gif')) or number(str-index(to-lower-case($value), '.png')) or number(str-index(to-lower-case($value), '.tiff')) or number(str-index(to-lower-case($value), '.tif')) or number(str-index(to-lower-case($value), '.bmp')) or number(str-index(to-lower-case($value), '.pct')) or number(str-index(to-lower-case($value), '.jpe')) or number(str-index(to-lower-case($value), '.jfif')) or number(str-index(to-lower-case($value), '.dib'))
        @return true
      @else
        @return null
  @else
    @return null