application to detect handwriting on a specific region of a sheet

I need to develop an app (preferably web based) that has the function:

1. Can take a photo (with tablet or smartphone especially IOS etc.)
2. Recognise the handwriting on the photo.
3. Put the it in a json file and to send it to a robot.

The keyword is robustness, I really need to detect surely the handwritten (so doing computer vision) and that we can translate into an instruction. Using OpenCv, Cloud Vision API google.

Sb has an idea on which platform to do (react, angular or react native, flutter etc...) or if there is already on open source app ?