I think it is necessary to credit problems you are sourcing from other locations.

There are quite a few katas on here that word for word are taken out of various programming contests where the original problem writes spend MONTHS writing the problems, generating multiple solutions in multiple languages, running through performance analysis and their hard work was not credited.

It only takes one line to quickly state where you are adapting these problems from.

Agreed, there needs to be more clarification about these cases since either direction could make sense and thus causes ambiguity.

I would do it in the Description. Jut be carefull the source does not reveal too many clues (or the complete solution ;-)

The description is, by large, a normal html fragment so you can add references the usual way.

I want to create katas out of interview questions that are already available on the web albeit with some alterations. I would like to credit the source. Is this needed? If so, what is the best place to do so?