Wikimedia Commons has a large set of curated, high-quality, free photographs: https://commons.wikimedia.org/wiki/Commons:Featured_pictures, https://commons.wikimedia.org/wiki/Commons:Quality_images.
There are also many, many gems among the 20+ million other free images at https://commons.wikimedia.org.
The site has an extensive category system that complements keyword-based search, e.g. https://commons.wikimedia.org/wiki/Category:Fruit.