I'm trying to fix some old (as in a few years old, not vintage) images taken by a friend, and have noticed something odd. While most of the pictures appear somewhat over exposed/have strange colours (possibly due to an effect implemented by the digital camera at the time), the thumbnails in each and every case are perfect (I've managed to extract the thumbnails as separate JPEG's.)
As such, is there a straightforward way or methodology for fixing the larger pictures using the thumbnails as a reference point? (Ostensibly for colours etc.) I have access to Photoshop but haven't used it extensively for many years (and even then didn't really use it for retouching work, at least not this sort).