I used these images gathered from the internet to make a screensaver on my Mac, like this:
1. Put images in a folder on Mac
2. Go to System Preferences/Desktop&Screensaver/Screensaver
3. Select "classic" screensaver
4. Under "Source" fill in the name of the folder from step 1.
5. To test, select Preview.
When activated, the screen saver cycles through all of the pictures in the selected folder, filling the screen with each picture, in turn.