Optionally update saved metadata when node is updated

Problem/Motivation

While going through and compressing images, removing the old larger file, then uploading a new file with the same JPG EXIF data, the old data is not updated. More specifically, what I mean is that I've changed exif_exposurebias to exif_exposuretime; however, the Exposure Bias value is still displayed, not the new value.

Example: 0/6 instead of 1/250 sec.

Steps to reproduce

I'm thinking the default for Exposure Mode was exif_exposurebias. I finally realized this and changed it. New nodes and images upload correctly.