Lorem Picsum - Lorem Ipsum... but for photos
FreeImages - Find and download free stock photos - all free for personal and commercial use
BlurHash - BlurHash is a compact representation of a placeholder for an image.
Unsplash - Unsplash is a website with high-quality free HD images. It has a catalog of more than three hundred thousand striking images that are neatly organized with tags. Read more about Unsplash.
PlaceIMG - Placeholder images for your project in progress. Custom URLs generate placeholder pictures in various sizes with categories and effects.
PlaceKitten - Dead-easy placeholder images. Of kittens.