Brian Balduf, CEO of VHT.com has recently pointed out that:
Stories like this definitely help in our argument that it’s not just an issue for photographers; it’s a consumer issue as well.
Yes, Zillow.com leaving listing photos up is an issue that has always irritated me. This is a property that we owned as a rental from about 2001 to 2009. Zillow still has my rental photos and the listing photos that were used in a sale of the property after we sold it.
Zillow isn't consistent about keeping listing photos though. Other properties we have owned in the Seattle area (same MLS as Snoqualmie) before and since the above property in Snoqualmie no longer have listing photos on Zillow. Also, the properties we own in Oregon do not have the listing photos on Zillow.
I think it should be up to all MLSs to make sure that no listing photos are ever retained by listing sites they feed.
Update Aug 29: As @Michael Allen points out in the comments this is a relevant article relating to this subject: https://national.wfgnationaltitle.com/2018/08/28/zillows-epic-listing-photo-battle-with-vht-enters-its-final-phase/