you must remove them. it's not your work, so all of that 'i-want-ppl-to-see-'em' is not alright.
dA is for you to post you own work, not someone else's.
you can put them on Photobucket (i guess that is where you found them).
it is the best to delete them from deviantART.
and trust me, i do not think the original artist would be pleased to see this.