Step 1: Check Your Pictures Size
Right click on the picture you want to use and click Properties.
If the size is bigger than 250k it must be made smaller.
Step 2: Compress Your Picture
Open your picture in Paint.NET
Click on File->Save As
name your file and hit Save
Scroll the quality meter until the size is just below 250k and hit OK.
Step 3: Move Your Picture Into the Right Place
If any part of that path doesn't exist, create the missing folder(s)
Move your file into the Backgrounds folder.
Rename the picture to be backgroundDefault.jpg
If UAC prompts you, click on Continue
Step 4: Enable Custom Backgrounds in the Registry
Type regedit and press enter
Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background
Create a new DWord Key named OEMBackground
Assign the value 1 to the OEMBackground Key
Step 5: Change Your User Profile Picture
Click on User Accounts
Click Change your picture
Click Browse for more pictures
Select your new profile picture and click Open
Step 6: Enjoy Your New Login Screen
Enjoy your newly revamped login screen