I first saw this beautiful piece of code enabling Before/After imagery on Jon Birdseye's website--http://jon-birdseye.squarespace.com/before-and-after.
The tutorial for installing it on the Squarespace platform is accessible via the link below. http://www.massexod.us/blog/how-to-create-before-and-after-images-for-squarespace
BIG THANKS to Anthony Kramer for writing the tutorial and modifying the code to make it so perfect! I'm looking forward to showcasing more Before/After imagery and attracting more retouching work!