This blog describes simple steps to change SAP screen with client/company logo which you see after logon to the system.
To perform this activity SAP client must be “open” and system should be set to “Modifiable” in SE03 , especially the “Customer Namespace”
Go To T-code: SMW0
Choose any of the entry and click on copy
Give name as Z<SID>
Click on Local object
Next click on import button and upload your image.
Next maintain mime types ( this is not necessary for all systems but may be missing in some systems)
Create a mime type for gif
Now go to SM30
Save the entries.
Log off and log in again to see the splash screen in your SAP system.