I believe you are talking about "Branding" a PC.
If so, then you need to find the Oemlogo.bmp and Oeminfo.ini, in the Windows/System or Windows/System32 folder.
Have a look at this site;
I would expect that such branding can only be done under licence from MIcrosoft.
pls let me know how i can change the image from Properties of My computer. We can put an image beneath the Computer image in General tab.