Open Source OCR Library:
1.ABBYY Mobile OCR Engine is a powerful software development kit which allows developers of mobile and small footprint applications to integrate highly accurate optical character recognition (OCR) technologies that convert images and photographs into manageable and searchable text. Toolkit supports the most popular mobile platforms and devices - iOS (iPhone) and Android. http://www.abbyy.com/mobileocr/
2.Tesseract is probably the most accurate open source OCR engine available. https://code.google.com/p/tesseract-ocr/