LoremFlickr
https://loremflickr.com/
A random picture matching the keyword dog, of 320 x 240 pixels.
https://loremflickr.com/320/240/dog
JSONでも出力できるらしい
https://babakfakhamzadeh.com/project/loremflickr-com/
https://github.com/MastaBaba/LoremFlickr-2