Do you want to customize login screen to see custom images that are related to your own company?
No problem, just put it into the Images folder (C:Program Files (x86)Acumatica ERP<Your Site Name>Icons) with the specific name pattern (login_bg<Number>.jpg).
Note that you can use many different images types, not only jpg. For example, dynamic .gif file can be super nice there. Check this link: Cinemagraph
Have a nice setup.