Thank you for reply, Phaethon!
Expecially on my last submissions that's also my case, and I prefered leave blank that entry. I have thinked about all that users who also do it.
I Would like to have clarifications about all stuff that can be considered derivation from something else.
For example suppose you want to submit images that you worked on but actually are not created or belongs to you at 100%, like avatars not directely drawn by yourself but reworked and modified. You added somethig to that images but something is not yours anyways because someone else has do that: what users should do for author entry? Shuld be leaved blank or you can considerate yourself as the author? Should you give credit to someone else if you know who created what you had worked on?