how to validate images in javascript

See this method:

<script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.8.2.min.js"></script>
<script> 
$(function() { // Call when page is fully loaded
    $("img.deferred").each(function(index) { // for each deferred image
        var tochange = this; // this is the image we will change
        var altsrc = $(this).attr('altsrc'); // here we store the actual image url
        var img = $("<img />").attr('src', altsrc).load(function() { //we try to load the actual image in an element
            $(tochange).attr('src', altsrc) // if we succeed, we can use the source for the actual image
        });
    });
});
</script>
Sample usage:<br>
<img class="deferred" src="http://www.nmh.ie/iopen24/images/content_images/other/warning.jpg" altsrc="http://www.jeremynoeljohnson.com/jimages/blogposts/apples01.jpg"><br>
<img class="deferred" src="http://www.nmh.ie/iopen24/images/content_images/other/warning.jpg" altsrc="http://www.jeremynoeljohnson.com/jimages/blogposts/NOTFOUND.jpg">

Notice the two img elements above. Both have a specific class, this makes them different from all others, and that is used by the jquery selector to find only them. The src attribute holds an url of a dummy static image, that is loaded by default. The altsrc (non-standard, custom) attribute holds the actual image url. The second sample element has this attribute set to a non-existent url. On page load all deferred img elements are parsed. The script tries to load the actual image file in a dummy element. If it succeeds, transfers the value to the actual image tag.

Hope it helps you.