Two out of the three posters did not read carefully:
I am considering images without human-made objects (i.e. cars, buildings, people...) or animals. For example, mountains, grass, sea landscapes... would work.
The question I would have for the OP is: are you looking for pictures of ugly subjects or ugly pictures of nice subjects? What does the adjective "ugly" attach to? Are you looking for what subjects people consider ugly, or are you concerned with how a picture of something nice can still be taken in an ugly way (as in technically poor, overprocessed, poorly composed...)?