This answer is more general than question specific. I will try to stick as much as possible with the problem statement.
Although there is a lot of on going research on recognition of hand written text, there is no full-proof method, which works with all possible problems.
The sample image you posted here is relatively noisy, with extremely high variance between the font of the same letter. This is exactly where it gets tricky.
I would personally suggest that once you have the bounding boxes around the text (which you already do), run contour extraction in all these bounding boxes in order to extract single letters. Once you have them, you need to figure out relevant feature/s that can represent the maximum variance (or at least 95% Confidence Interval) of the particular letter.
With this/ese feature/s, you need to train a supervised algorithm, letters as training data and their corresponding value (for eg. actual values) as labels. Once you have that, give it some data (the easiest and most difficult cases) to analyze the accuracy.
These links can help you for a start :
One of my first tools to check the accuracy with the set of features I use before I start coding: Weka
Go through basic tutorials on machine learning and how they work - Personal Favorite
You could try TensorFlow.
Simple Digit Recognition OCR in OpenCV-Python - Great for beginners.
Hope it helps!