all my work is cc-by-sa ( except for commission work and work for hire )
But i deal is imaging from spacecraft and not dungeons

as above UNLESS there is a cc license ( research this there are a few different ones )
or the GPL ( but there are a few of these gpl2 and 3 and the lesser versions )
or the MIT ( as in the school ) or the Apache license --but these are more for software and programs but covers images used in them

you need permission

now some like the cc-by-sa you can use without permission BUT!!!!!!! you MUST give credit to the artist!!!!!!