Possibility of fading in

[developer2323]

Possibility of fading in

[mikegreiling]

If you don't care about IE9 support, you could try CSS animations:

img.parallax-slider {
    animation: fadein 2s;
}
@keyframes fadein {
    from { opacity: 0; }
    to   { opacity: 1; }
}

Or, you could use JavaScript:

$(function() {
    // after parallax plugin is initialized...
    $('img.parallax-slider').hide().load(function() {
        $(this).fadeIn('slow');
    });
})

Note, you may need to fidget with these a bit. I haven't tested them, but this should get you started.