You must obtain written permission from the proper and legal owner of any work which you wish to use, credit alone does not replace this requirement. Failure to obtain proper permission for the use of works protected under copyright can leave your DeviantArt submission vulnerable to being removed following a claim of infringement against it.
Explicit permission is not required when you choose to use valid stock resources. Please check your sources carefully to ensure that they are valid stock and please be certain to obey all rules, terms and conditions which may be attached to that resource.
Read about art theft and our copyright policy in The Art Theft Discussion.