When scanning prints, negatives, or slides, the metadata within the image is likely to be incorrect, as the date is that of the scan rather than the date when the photo was taken. In addition, you may want to insert additional metatags, so the information stay with the image rather than externally in some other format. This is not a comprehensive list of metatags, just the most commonly used in the tools I examined.
Being linux based, I'm looking at these tools (as of Ubuntu 15.10):