How can I change the background images and logo of the Login page?
In order to replace the background images of the welcome page, you need to place them in the folder: themes/default/statics/img/welcomewp/
The image back.jpg size must be min 1920×1080 and the names and extensions must match exactly as shown in the list above.
and logo.png size must be min 300px
However, if you want a more flexible configuration of this back.jpg and remove these restrictions, then you need to edit the following file: themes/default/apps/guest/content.phtml