How do I add rollover images to a wordpress post?

Hi,

I am trying to add some rollover images to a post on my self-hosted wordpress blog. I looked in a variety of places online for instruction, but none seem to target what I need to accomplish.

I have 5 ‘before & after’ style images that I want to include in the post. I want to set it up so that when people look at the images in my post it looks like 5 regular ‘after’ images, only when the user hovers over them, he/she can see the ‘before’ images. This post is for my portfolio and I am trying to showcase an image before and after I edited it on Photoshop.

I saved the ‘before’ images as “my-image.png” and the ‘after’ images as “my-image_over.png”. All the images are the same size and I uploaded them to my blog via the ‘Media’ tab.

Do any of you know how to make this work?

Thanks so much in advance!