Convert THUMBDATA3-- to JPG

There is really no way how you could get a JPG picture out a THUMBDATA3-- file. It is just a cache file that contains thumbnail data for a picture that exist, or once existed in your Android phone. The problem is a .thumbdata3-- file contains data from ALL pictures, not just single one, so there is no way how to get a single one, even in thumbnail form.

Simply put, it is impossible to convert THUMBDATA3-- to JPG directly.
Thus, there is no so-called thumbdata3-- to jpg converter or a free online .thumbdata3-- to .jpg converter to be found.