Resources for the series MEDIUM are scarce, few and far between. Even at the height of the series popularity there wasn't a lot of content created for it because of a lack of an active fandom. That said, here are a list of visual resources for screencaps and promotional images for the television series that are still active since the show's cancellation in 2011.
Promotional Press Release Images by NBC and CBS
High Quality Screencaps by Captacular.com
Middle to low quality screencaps
MEDIUM fansite (French)
MEDIUM on Netflix.com (HD Steaming and DVD for rental with membership)
Medium Moments @tumblr.com
She Sees The Truth @tumblr.com