"ThingLink http://thinglink.com/ is one of my favorite tools that I've reviewed on Free Technology for Teachers. The free service allows you to make any image interactive by adding digital pinmarks to it. Those pinmarks can include text, links, videos that are revealed when some touches those pinmarks while viewing your shared images. The service previously worked in your iPad's web browser, but now this great service is now available as a free iPad app http://ow.ly/luKR0 ; too."
Via John Evans