http://www.speakingimage.org/

Speaking Image (www.speakingimage.org) is a tool to create interactive images that can be collaborated and shared with others.  It is rather technical so may be best suited for high school students.  

Images are uploaded to speaking image, you can add text, and other pictures to help to explain or draw attention to particular aspects of that photo.  For example, if you were doing a social studies lesson on politics and you were explaining the process of government, you could upload a picture of the legislature and then draw attention to the different roles of say, the premiere, the speaker, ministers, MLA's, etc.  

For students that are visually impaired, learn better by visual stimulous, have troubles paying attention, or having difficulties reading and writing, this resource can be an effective alternative to both teaching and assessment for students.