joker95,
попробуйте так
<!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>
$(function(){
$(".ob_img").each(function(indx, div){
var img = $("img",div), width = img.width();
width && width > 100 ? $(div).append('<div class="photo_numb">this is </div>') :
img.on("load", function() {
img.width() > 100 && $(div).append('<div class="photo_numb">this is </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>
<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>