gistfile1.txt

var seen_images = [...]

var process_image = function() { /* render */ };

var find_image = function(page_num, callback) {
    $.get('url', {page: page_num}, function(image_list) {
        var new_image_found = false;

        for(var i = 0; i < image_list.length; ++i) {
            if(seen_images.indexOf(image_list[i]) == -1) {
                new_image_found = true;
                callback(image_list[i]);
                break;
            }
        }

        if(new_image_found === false) {
            find_image(page_num + 1, callback)
        }
    }
}

find_image(params, process_image);