Perhaps desaturate all the images that will be used in the background, this will draw the focal attention to the login form and social connection options without being too distracting.
I like the concept of having the background change each time the page is refreshed, or each time a login attempt Is made. Also, perhaps style the users “Username” and “Password” field to the same style of the users disay picture/ avatar.
Here are a couple images of the OSX login screen for reference and inspiration:http://1.bp.blogspot.com/-e9hKBw3TzM4/Tic1_JZ2EAI/AAAAAAAAAPw/8zjANCBNYSw/s1600/login.png
Thanks for the feedback, That’s usefull. Was thinking of a OSX stylisch form myself aswell