It might be easy, but until iOS 8 is released, non-Safari JS still takes a performance hit. [1] You may want to take a look at the Tesseract library and Objective-C wrapper. [2]

[1] http://9to5mac.com/2014/06/03/ios-8-webkit-changes-finally-a... [2] https://github.com/ldiqual/tesseract-ios

edit: Looking closer at this lib, impressive. Might give it a go.

Doing anything to a live video feed in JS on a phone probably won't be very feasible except for extremely low resolution video.