You need to register (free).
You upload your own picture to the web site and are then able to crop to use just part of the picture if you want to.
You then place the mouth area on the graphic - you can use as many of these as you want to i.e. you can have more than one person in the graphic.
You then record the sound and your video is made. These can be embedded into the class wiki, blog etc.
Students will love making these as part of a presentation about a research project for example if students are studying about another country they could use a picture of a person from that country and then have them speaking about the food that they like to eat or something similiar. Young children could do a news topic for others to look at.