How to Change the Ugly Guy Picture on Windows 8 Ctrl+Alt+Del Login Screen

The "ugly guy" image is stored as a resource inside %WinDir%\System32\AuthExt.dll. Thus, in order to change the picture, a resource editor such as Resource Hacker (known as ResHacker or ResHack) has to be used.

1) Run Resource Hacker or any resource editor such as Restorator, ResEdit, XN Resource Editor and etc.
2) Open %WINDIR%\System32\AuthExt.dll file.
3) Expand Image tree.
4) Expand 1001 tree.
5) Right click on 1033 (for English – other language may have different code), and select Replace Resource.

Click on Open file with new resource, and select a JPG image which has the resolution of 1280×1024 pixels.

Then, enter the following information:

Resource Type: IMAGE
Resource Name: 1001
Resource Language: 1033 (depends on your OS’s language and should be the same with original code)

Click Replace to make the change.

Note: The steps for different resource editor may be different. If your resource editor does not have replace function, just delete the "1001" resource branch, and then add a new one with the same settings of "IMAGE, 1001, 1033".

Source: http://www.gadgets5.com/2011/05/how-to-change-the-ugly-guy-picture-on/