<div id="123" data-img-flag="1">
<image src="abc.png">
</div>
<div id="432" data-img-flag="0">
<image src="abc.png">
</div>
<script>
alert($(popImgId).data('img-flag')); // when we use data function to get the data attribute value wll get all time value loaded at the time of DOM loaded
alert($(popImgId).attr('data-img-flag')); // value will get lates. If we change/update value using jquery will get updated value
</script>