I'm glad that you like it:)
Well some of them had really bad writing but sometimes some other things can be factors like at this sample below:
Because it has this black spot in the lower left corner and I was cutting the edges until it comes to first black pixel, it's recognized as 9 😢
It's nice to see that preprocessing was responsible and not the algorithm itself. With some more advanced method to replace the simplest thresholding, this becomes useful ;)