So using the MMM-iFrame you can get google photos onto a mirror

Firstly you need to get this add on for slides https://chrome.google.com/webstore/detail/photo-slideshow/llgeanpccblagafdmfalehmopdbakhol?hl=en
This allows you to auto generate a slides presentation from a photos album

Next copy the link into iFrame (file -> publish to web)

Set you size position

And here is a result

Hope you find it useful!