In my knowledge, there is no tool to make change the splash screen automatically. However I would like to ask if there is a way to do that. Say I have a folder of images and I want each of them appear to be splash screen randomly every time I log on. Is it possible? I think it would change your splash screen before shutting down is a solution.

Oops, it seems that I post in wrong section. Can you move it for me? Thank you.

moved as requested

I would suggest using a Shutdown or Pre-Startup script to do this. Execution of the script itself can be done in System Settings. You'll need to work something out for the randomisation part though.

Do you know what command to change the login splash screen so that I can write to the script? It doesn't really need to be random, but it should be able to change the picture everytime I log on.

This would depend on the splash screen theme which you have selected. It should just be a case of overwriting the image file which your system uses though.