Speaking for myself only, even for charitable situations, I ask permission from the original artist to use their design, for anything beyond strictly personal use (birthday card for grandma, etc.).
I do this that so the artist whose work I am borrowing, feels valued and appreciated for sharing an idea that helped me when I needed inspiration. UKWIM?
As others have already mentioned, CASEing for publication, personal gain, or contest entry, without seeking and receiving permission, would be an issue.