Yes - but the downvotes will remain associated with the observation until the voter chooses to remove them, so that does still serve to indicate that the observation has (or had) DQA issues. However, I agree that this is not sufficient. More needs to be done to explicitly encourage users not to use other people’s photos - and also to encourage the other people to join iNat instead of allowing their photos to be copied.
PS: there’s another thread that deals with essentially the same issues that you might be interested in.