Edit in JSFiddle

$.getJSON('http://www.reddit.com/user/reset_by_peer/m/imaginary/.json?jsonp=?&show=all&limit=300', function (data) {
    $.each(data.data.children, function (i, item) {
        IsValidImageUrl(item.data.url, function (url, isvalid) {
            if (isvalid) {
                $('<img/>').attr('src', item.data.url)
                    .width(500)
                    .appendTo('#images');
            }
        });
    });
});


function IsValidImageUrl(url, callback) {
    var img = new Image();
    img.onerror = function () {
        callback(url, false);
    };
    img.onload = function () {
        callback(url, true);
    };
    img.src = url;
}

Cool Images
<div id="images"></div>

body {
    margin: 15px;
}
img {
    display: block;
    padding: 3px;
}