There are many libraries available for extracting text from images.
Tesseract and Abby are the best OCR SDK's I have used. The main advantage with Abby SDK is that its results are nice as compare to Tesseract . And the only disadvantage with it is that it is purchasable . While the main advantage in Tesseract is that it is open source and you can improve its result by using any image processing library.
1) Abby - https://github.com/abbyysdk/ocrsdk.com
it uploads the image to its server, converts image to text and downloads the result
2) Tesseract - https://github.com/nolanbrown/Tesseract-iPhone-Demo/tree/master/OCRDemo
It converts the image to text using tessrect sdk. Not as accurate result as Abby but does not require internet connection.
3) Tesseract + OpenCV - https://github.com/pablosproject/iPhone-OCR-Tesseract-and-OpenCV
Probably the best sdk I found so far to read image without internet connection. Advantage of this code is it integrates OpenCV too, thus you can add algorithms like blog extraction algorithm and hough transform to increase the accuracy of result.
I hope it helps.
