This is a list of iOS image filtering, processing, OCR, utilities and helper libraries and frameworks that I have come across for iPhone and iPad development and thought that they may be useful in one places:
1. GPU Image
By Brad Larson, GPUImage is a fantastic fast processing library to apply gpu accelerated filters to both live camera feed, movies or stills. It works on iOS 4 and above. It includes a range of filters such as Sepia, Grayscale, Blur but you can write your own easily.