Serving images across mobile and web

I need to build a web portal that uploads images to a database. These images will be displayed in an android app, and the web portal.

The common method i use when dealing strictly with apps is as follows:

-compress the picture

-encode it to a Base91 string

-send to server for storage

How do i achieve this in the context of a website(using javascript or python)? particularly the encode/decode(Base91) part.

ps: My experience with web is very basic.

Please let me know if more clarity is needed.