C/C++/Objective-C text recognition library

Here is an interesting article on how to extract numbers from picture.

The author collects large number of samples to train his neural networks algorithm and I believe doing the image processing with OpenCV.

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/

The most famous one is Tesseract OCR developed initially by Motorola and later become open source. It is also promoted by Google.

There are a few more, perhaps not as famous as Tesseract: http://en.wikipedia.org/wiki/OCRopus http://jocr.sourceforge.net/