Have you tried removing the desktop picture?
I'm a little confused about your message.
So the screen is flashing before you log in? how can you see a desktop picture before you log in?
Please clarify and then I can try and assist you further.
Best phone camera 2017
Stunning new film posters by Hattie Stewart, Joe Cruz & more
iPad Pro 10.5in (2017) review
28 astuces pour profiter au mieux de votre iPhone