The Virtual Lightbox is a software tool for comparing images online. It exists in two versions, an application and an applet (both programmed in Java). The applet version, which is newly developed, furnishes what we believe to be an extremely flexible environment for online image comparison. Its primary audience is developers who wish to add an image comparison tool to a Web-based image collection. Simple server-side scripting allows users to populate the Lightbox applet in any number of ways. The application version, which was developed earlier, allows users to share images in peer-to-peer fashion: all users participating in a common session see the same images in the same on-screen configuration at the same time. Movement of an image and other operations are all globally propagated in realtime. Thus the application version functions as an image-based whiteboard. The Lightbox began development in July 2000, first funded and supported by the Center for Computational Sciences at the University of Kentucky and the Research Experiences for Undergraduates program of the NCSA's Partnerships for an Advanced Computational Infrastructure, before moving to MITH, where we released version 2.0 in February 2004.