Returns a specific image $file object by filename. If no filename is given, the first image will be returned.
<?php if($image = $site->image()): ?>
<img src="<?php echo $image->url() ?>" alt="">
<?php endif ?>
<?php if($image = $site->image('myimage.jpg')): ?>
<img src="<?php echo $image->url() ?>" alt="">
<?php endif ?>