The majority of Zillow's photos come from real estate agents or homeowners, who either upload the photos to Zillow or provide them in a feed of listings. This often happens when a home is listed for sale. Additionally, Zillow publishes aerial photos from Bing and Street View photos from Google Maps.
In addition, as part of a limited test to improve the overall quality of data and images available through Zillow, we recently uploaded photographs of home exteriors in select Seattle neighborhoods. These photos were collected from sidewalks or the street, and offer a similar perspective to images typically available through Google Street View and, often, county and local assessor offices.
To remove photos uploaded by an agent or homeowner, or to remove one of the test photos, see the help article for how to add or remove photos of your home.