multiple digit detection
For this problem, I could provide you with 2 approaches, 1. Naive approach 2. Actually used for object detection. 

Talking about the Naive approach, in this approach we can build an end to end pipeline for digits extraction using the following pipeline:


Take images and clean image (maybe take threshold or tune brightness and contrast to remove noise and artefacts)
Take the cleaned image and find the contours of the text inside the image over the text and then finally detect the numbers.


This is certainly one solution but has a lot of complications involved alongwith.
To solve this problem, here is other approach that is used in actual OCR. For this, we follow this pipeline:


Take a cleaned image 
From left to right (In the order of actual human reading pattern) run a sliding window and after Non-max suppression, find the text.
For each text found using the sliding window, run the prediction and store the prediction in the required format of your choice.


Although this too contains a number of complications and problems related to a number of other problems, this is still the best method and can be tuned as per the requirement to extract the exact required text.