CNN for Digit Recognition with MLpack C++

I need a CNN for digit recognition made with mlpack in C++, other dataset than MNIST. I already implemented one with the MNIST dataset, but the accuracy is low for numbers that are slightly different from the MNIST dataset. I need this for my augmented reality project. Besides the implementation, I need a clear and explicit documentation, so I could understand everything. I am new to machine learning, so I want a documentation friendly for beginners, with network depictions and other helpful aspects.
I found this dataset, maybe it would help.
https://www.kaggle.com/datasets/kshitijdhama/printed-digits-dataset