Hi Maarten,
Adobe Photoshop elements 12 (individual license) requires sign in /activation if you have installed individually however you can suppress the sign window using Adobe provisioning toolkit
In case you have Adobe volume license for PSE 12. Please visit the link below to find the workflow.
https://helpx.adobe.com/photoshop-elements/kb/photoshop-element-12-silent-install.html
Thanks,
Ashish