Image Tween with Element.crossfade for MooTools
Element.crossfade is a MooTools extension to simulate a tween for background-image element’s property.
The syntax, in this new version, is very clear:
document.id('el').crossfade('end_image.jpg');
Just remember your element position property in CSS should be expressly declared (as absolute, relative or fixed), don’t leave it blank.
Note: you can customize the fade behavior by setting tween properties
document.id('el').set('tween', {duration:5000});
These will be inherited by ‘crossfade’ animation.