I want my users to be able to login using all common OpenIds. But there seems to be a forest of clauses on how to use logos from google, facebook, yahoo and twitter.
Actually I'd prefer a wider button with the text on it, but it seems that all these buttons don't have the aspect ratio. And some of them I am not allowed to scale. 
Also some pages switched to javascript buttons which seems incredibly stupid, because that causes the browser to download all the javascripts and the page looks like 1990 where you can watch individual elements loading.
So finally I surrendered and went for the stackoverflow approach of using square logos with the text "login with" next to them. But now I can't find an official source for a square yahoo icon.
The question: Can you recommend any articles or do you have any tipps on how to make OpenId look uniform?
And: Have you seen an official source for a square Icon that I'm allowed to use?
PS: I'm using python-social-auth for Django.
You could simply use the yahoo site's favicon. It's already squared and gets as close to official as it can get.
How to make most common OpenID logins look the same?