Php/Websites are unknown territory for me and the picture is still ambigous. I am afraid the best fit heavily depends on your architecture and use case.
Though, from an architectural perspective it seems odd to mix code and content. Usualy code or compiled binaries (the part that is identical for each customer) belong into the image, content (which is different per customer) usualy is held externaly (like in a db, fileshare, cdn or a simple webserver for static content).