I see absolutely no value in a post that just posts someone else's pictures with no text. This is supposed to be a content creation network, and if a post doesnt have at least some original content then it shouldnt be here. Ive created posts with my own photos and limited text and also used free stock photos in longer posts as i dont have relevant images myself. Both of these are valid use cases. In cases where i have seen images used with no source and are blatently there to just try to get a few upvotes i have been commenting with the source and then notifying steemcleaners.