How to prove the authorship of works?

Question

Copyright

Looking for a job. Completed 8 test tasks, all free. All the time, someone did not like something, arguing "We have already found another applicant." In general, no feedback. I decided to indicate in the responses that I will only perform test tasks for a fee. Faced the problem "We do not believe that all the works belong to you." How to prove your authorship in addition to commits on github?

Answer 1

The direct answer to the question is your copyright in the layout of the live site used.
But in general, the policy "do test tasks for money" is bad.
It is better for yourself in each specific case to assess the prospects of the employer - and either do it for free - or refuse correspondence assignments.
In my experience (if we don’t talk about junior vacancies) - the task is usually asked either by very large offices, or by small firms with great pathos.

Answer 2

Faced the problem "We do not believe that all the works belong to you."

That is, your work is so cool, but you look like 12 years old?
;)
I don't see any other reasons.
Do they not believe their luck that too cool special came to them?
The reason is something else.
As an option - you look 12 years old, therefore.