Posterous has released an update to its utility for posting photos and videos to Posterous.com adding background uploading on multitasking-capable iOS 4 devices and updated graphics for the iPhone 4 Retina Display. PicPosterous allows Posterous users to upload photos and videos to Posterous from the camera or the device’s saved photos library, either creating new albums on Posterous or adding photos to previous albums. Users can also delete…