Super nice feature in Windows 8.1

1. Swipe in from the right and select Settings, and then Change PC Settings Change pc settings
2. On PC settings select PC and devices PC and devices

3. Then select Lock screen

image
4. Find the Play a slide show on the lock screen option and move to the right to turn it on play a side show off
Play a side show on
5. Then choose the locations where you want your pictures from.  You can also add folders here choose pictures location

See more detail at See pictures on the desktop, Start and the lock screen

Get more help for Windows 8.1

Rob

PS the above works for Windows 8.1 as well