joker95,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.photo_numb:after{
content: "big"
}
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
<script>
$(window).on("load", function(){
$(".ob_img").filter(function() {
return $("img",this).width() > 100
}).append('<div class="photo_numb"></div>');
})
</script>
</head>
<body>
<div class="ob_img">
<img src="http://i.i.ua/photo/images/pic/6/4/1008546_75741f3e.jpg" alt="">
</div>
<div class="ob_img">
<img src="http://pda.maybe.ru/p/177/176879/t17638688.jpg" alt="">
</div>
</body>
</html>