How to make an interactive comparison of images thingy?

Mehta23 · Apr 4, 2014

Something like this : How London is experiencing an unparalleled boom in tall buildings

I've seen them before and just wanted to know if it was easy to make one myself.

Slug · Apr 4, 2014

Mehta23 said:
[...] just wanted to know if it was easy to make one myself.

Probably, if you can code Javascript. From looking at the frame source it appears to be done with a combination of bespoke style sheets and JS.