Scanning in an image and converting it to text is relatively straightforward in Linux provided you have the correct software installed. I plumped for Tesseract as it was reputedly the best command line OCR program but I also wanted to have a graphical user interface with it so I used gImageReader as a front-end to Tesseract.
Here's how to install both of them.
Firstly, install tesseract (and the associated language files if needed):
sudo apt-get install tesseract-ocr
Install a language file (e.g. -eng, -deu, -fra, -ita, -ndl, -por, -spa, …)
sudo apt-get install tesseract-ocr-eng
Next, install gImageReader as a frontend to tesseract.
Add the application repository:
sudo add-apt-repository ppa:sandromani/gimagereader
Update the repository sources
sudo apt-get update
Install the application
sudo apt-get install gimagereader
Now you should be ready to go. gImageReader can be accessed on your graphics menu. Happy Character Recognising!