[ocrcustomserver]

The reason is that online OCR (this particular case) is entirely different from offline OCR.

Online OCR is when you input the strokes directly on the tablet/phone, so it becomes a sequence of XY coordinates with an associated timestamp. It takes into account where you start and where you end the stroke on the canvas, along with the intermediate points (information galore).

Offline OCR is when you take a photo of your handwriting in your notebook, so you just get the raw pixels of a image. In offline OCR, you'd also have to properly segment and binarize the image before the OCR step.

With that being said, tesseract (version 4) uses an LSTM.