If you want to display before and after images in your website, it will be possible to do it with WordPress out of the box. So, a plugin such as this TwentyTwenty plugin by Corey Martin will make it possible.
This plugin takes advantage of the clip property within CSS by stacking two identical-sized images on top of each other. This clip property will allow the image to show through the container.
The slider is responsive and it uses custom movements events in within the JQuery Move library to support 1:1 slider movement even on mobile devices.
It is easy, simple to use, and do what it does best.
Read the rest of the review here: http://wptavern.com/display-before-and-after-images-in-wordpress-with-the-twentytwenty-plugin