Word Lens is a free app for iOS and Android that translates printed words instantly. You open the app, select the language and point the camera at the text. What appears on your screen though, is not what the camera sees, it's the translation. (Android version)
I can't vouch for the accuracy of the translation, and I would hate to try to read a whole book by waving my phone over it. If you are a student who is still learning English though, this app could help you check your understanding, or give you the translation of the word that is stumping you. This will have classroom applications for students new to English and will potentially also have applications in World Language classrooms.
Word Lens currently offers translations to and from English for the following languages: Spanish, German, French, Italian, Portuguese and Russian. Google recently bought Word Lens so all of the languages are now free and I hope the list of languages will continue to grow. I think it is also likely that we will see the functions of Word Lens built into the next iteration of Google Glass.
If you are a teacher concerned about how this technology will impact student language development I would encourage you to read my earlier post about Google Translate. The genie is out of the bottle, and now she can take her pick of languages to play with.