I'm new to video processing and I'm wondering what libraries I can use to do things like detecting letters, drawing boxes around them and so on. If you can name me a couple of good ones, I'd appreciate it very much!
OpenCV: (Open Source Computer Vision) is a cross-platform library of programming functions for real time computer vision.
It provides interfaces for both C and C++ programming laguages.
As for detecting the text region and drawing boxes around it, you can take a look at this article, which explains how to do this stuff using OpenCV. For better OCR capabilities I think that tesseract is the best open source tool available right now.
I've worked on a similar project some time ago and used OpenCV to detect the text region and then tesseract to do proper text recognition.