They are a dime a dozen in the Google Play Store.
You can find photos of cityscapes, landscapes, people, cars, and other such things.
You can also add parameters to the search to ensure you find the type and resolution you want.
Plus, it's free and it probably came with your phone anyway.
Some subreddits we recommend are r/itookapicture, r/photocritique, r/astrophotography, and r/earthporn.
There is an optional Reddit Gold subscription that removes ads and adds some additional features.