Arrastra una imagen al label con el input[type="file"] y el js hará una cargar previa... :P

dropimage.css

.dropimage {
    position: relative;
    border: 4px dashed grey;
    min-height: 150px;
}

.dropimage:after {
    color: grey;
    content: "Drop image";
    font-size: 30px;
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
    z-index: 1;
}

.dropimage input {
    left: 0;
    width: 100%;
    height: 100%;
    border: 0;
    margin: 0;
    padding: 0;
    opacity: 0;
    cursor: pointer;
    position: absolute;
    z-index: 2;
}

.dropimage img {
    width: 100%;
}

dropimage.jquery.js

$('body').on('change', '[type="file"]', function(eve) {

    var img = $(this).parent().find('img'),
        label = $(this).parent(),
        reader = new FileReader();

    console.log([img, eve, label, reader]);

    reader.onloadend = function() {
        if (img.length) {
            $(img).attr('src', reader.result);
        } else {
            $(label).css('background-image', 'url(' + reader.result + ')');
            $(label).css('background-repeat', 'no-repeat');
            $(label).css('background-size', 'cover');
        }
    }
    reader.readAsDataURL(eve.target.files[0]);
});

dropimage.js

document.addEventListener("DOMContentLoaded", function() {
    [].forEach.call(document.querySelectorAll('.dropimage'), function(label) {
        label.onchange = function(e) {
            var inputfile = this,
                reader = new FileReader();
            reader.onloadend = function() {
                var img = inputfile.children[1];
                if (img !== undefined) {
                    img.src = reader.result;
                } else {
                    inputfile.style['background-image'] = 'url(' + reader.result + ')';
                    inputfile.style['background-repeat'] = 'no-repeat';
                    inputfile.style['background-size'] = 'cover';
                }
            }
            reader.readAsDataURL(e.target.files[0]);
        }
    });
});

dropimage.phtml

<label class="dropimage">
	<input type="file" name="imagenes[]">
	<?php if ($partida->fotos): ?>
		<img alt="..." src="...">
	<?php endif; ?>
</label>