Recognize numbers in images


Why not look at using an open source OCR engine such as Tesseract?

C# Wrapper for Tesseract

Java Wrapper for Tesseract

While you might not consider using a third-party library as implementing it yourself, there's a tremendous amount of work that goes into just integrating the third-party tool. Keep in mind also that something that may seem simple (recognizing the number 5 versus the number 6) is often very complex; we're talking thousands and thousands of lines of code complex. In the least, look at the source code for tesseract and it'll give you a good reason to want to leverage a third-party library.

Here's another SO question that'll give you some ideas about the algorithms involved:


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Updated on July 09, 2022


  • svens
    svens 6 months

    I've been searching for resources for number recognition in images on the web. I found many links providing lots of resources on that topic. But unfortunately it's more confusing than helping, I don't know where to start.

    I've got an image with 5 numbers in it, non-disturbed (no captcha or something like this). The numbers are black on a white background, written in a standard font.

    My first step was to separate the numbers. The algorithm I currently use is quite simple, it just checks if a column is entirely white and thus a space. Then it trims each character, so that there is no white border around it. This works quite well.

    But now I'm stuck with the actual recognition of the number. I don't know what's the best way of guessing the correct one. I don't think directly comparing to the font is a good idea, because if the numbers only differ a little, it will no more work.

    Could anyone give me a hint on how this is done?

    It doesn't matter to the question, but I'll be implementing this in C# or Java. I found some libraries which would do the job, but I'd like to implement it myself, to learn something.

  • svens
    svens almost 13 years
    Thanks for the tip. Actually I'm not that good in C/C++ and there's a lot of code. I'm still hoping not having to try to understand a whole OCR software project, just for learning number recognition.
  • Keith Adler
    Keith Adler almost 13 years
    This will remove the need for you to use C++ ... the C# wrapper is pretty straight-forward. Unless you want to become an expert in machine learning and image optimization you really don't want to try to roll your own OCR solution.
  • rook
    rook almost 13 years
    +1 Tesseract is awesome. You can use any language you want as long as you call it on the command line.
  • Keith Adler
    Keith Adler almost 13 years
    You can use it as a DLL as well with not much effort so no command line necessary. It comes with this out of the box as they say in their release notes.