PicMonkey includes an integrated stock photo library powered by photos from Unsplash. All photos published on Unsplash can be used for free.
You can use them for commercial and noncommercial purposes. You do not need to ask permission from or provide credit to the photographer or Unsplash, although it is appreciated when possible. More precisely, Unsplash grants you an irrevocable, nonexclusive, worldwide copyright license to download, copy, modify, distribute, perform, and use photos from Unsplash for free, including for commercial purposes, without permission from or attributing the photographer or Unsplash.
This license does not include the right to compile photos from Unsplash to replicate a similar or competing service, or to represent any photo as your own work.