I have noticed that when I update comments (for example) on a photo the XMP/EXIF data is written to the jpg file (as per my jAlbum settings) but the file modified date does not change (Windows).
Is this by design as it makes tracking changes at the file level more challenging?
Just a guess, but if the file modified date were changed, then the next time you made the album, jAlbum would think that the file had been changed since the previous build, and would reprocess it. Then it would write out the metadata again, and touch the file date again.
In short, it would reprocess the images every time you made the album!
I don't quite understand what you mean. I am suggesting that the jpg modfied date is changed when the image comment/title etc is changed through jAlbum. It already updates the image with the EXIF/XMP updates from this change to title/comment and this happens at the edit time, not the album creation time.
I can't see why this would update everytime the album is created as this EXIF data is not written out to jpg's everytime the album is re-created but but only when individual photos have changes made to them.
jAlbum avoids updating the last modified date to the source images when you simply change XMP metadata. The reason for this is that jAlbum uses the last modified date to determine whether to reprocess the image or not. jAlbum tries to avoid reprocessing images during "make album" operations to save time.