Change of Branding image in Welcome page of portal

  In simple, search for the image file with the name "branding_image" in the usr folder. Replace that image file with your company logo file with the same name.

Restart the server which inturn will change the image of welcome page.

or else

You can just enter the location in the below parameters.
In config tool.
Go to:
-> Global configuration.
-> Server.
  -> Services
   -> UME Provider.
       -> ume.logon.branding_image
       -> ume.logon.branding_text

try to copy the image to :
/usr/sap/<SID>/JC00/j2ee/cluster/server0/apps/sap.com/com.sap.security.core.admin/servlet_jsp/logon/root/layout