It depends, do you have a link with an image setup as an example? I can take a look at it and tell you the best way to go. You could probably just create a new class and add something like this –
-moz-transition: all 0.1s ease-in-out;
-webkit-transition: all 0.1s ease-in-out;
transition: all 0.1s ease-in-out;
That’s the same code for the featured images I believe…