Bricks of the Past - Rephotography at the Spokesman-Review

Riverside Avenue in 1909 and Today--where did all the people go?

Our local newspaper has been dipping into its archives for content more and more lately. It is a welcome trend for local historians. The latest offering is Bricks of the Past - A Then & Now gallery. Readers of this blog now what a sucker I am for rephotography projects, and this one is very nicely presented, with a slider bar at the bottom of each image to shift between past and present.

Does anyone know what software they used to do this?