On the /user edge, user pictures url are not returned by default, and when users ask for it, the response image is not in biggest format. This query should get the largest user pictures associated with post :

	/user{picture.type(large)}

There are other use cases where this syntax applies as well

• get comments of a feed

	/feed?fields='from{picture.type(large)}'

• get feeds of an user

	/userid/feed?fields={from{picture.type(large)}}

Examples tested with Facebook Graph API > v2.0, using Graph Explorer and PHP SDK.