Why not test it out? The link you sent seems good?
I can't tell you any more answers, but I can give you some more information to use when searching google?
The science of detecting characters in images is called OCR, see for example: https://en.wikipedia.org/wiki/Optical_character_recognition
MNIST have a large database of handwritten numbers, and if you search for it you will find a lot of good resources / algorithms. http://yann.lecun.com/exdb/mnist/
Personally I think I would have used PCA (https://en.wikipedia.org/wiki/Principal_component_analysis) to detect them. But the link you provided had a much simpler solution, and as you know KISS? (https://en.wikipedia.org/wiki/KISS_principle)
// Fredrik Löfgren, TC and OC member 2016 / 2017