Non velocity.js tips
css3 - with -webkit-/-moz-/-o-
Works on chrome only (I think), you need to rewrite it (for that you can find a few help here: http://www.w3schools.com/css/css3_transitions.asp and on the Internet :) ), but the second example is do the same what you need (works with onhover in chrome)
http://css-tricks.com/webkit-image-wipes/
If I know very well, the mask attribute only works in safari and chrome and maybe in opera too.
jQuery
Something like you need: http://jquery.malsup.com/cycle/wipe.html
Maybe you search for this: Nivo slider effectslicedownright
Other which can useful:
Jquery image transition left to right and fade in, in a slideshow
CSS fade left to right
Fade effect left to right on a image
CSS Fade Between Background Images on Hover
In my opinion, if there are one which works, use that, don't write another one. Mostly you can find a lot of result for this, if you search for this: jQuery fade left to right | jQuery fade left to right between two images
velocity.js tips
Maybe the answere were be here: http://julian.com/research/velocity/ at the fade & slide section
Or here: http://www.smashingmagazine.com/2014/06/18/faster-ui-animations-with-velocity-js/ the stagger section looks like that.