Add a class to all images that are aligned left or right

snippet.css

img.float-left {
  float: left!important;
  margin: 6px 12px 10px 0!important;
}
img.float-right {
  float: right!important;
  margin: 6px 0 12px 10px!important;
}

snippet.js

$('#content img').each(function() {
  var $this = $(this);
  if ($this.css('float') === 'left') {
    $this.addClass('float-left');
  }
  else if ($this.css('float') === 'right') {
    $this.addClass('float-right');
  }
});