> I frequently use the Thumbs Plus "Modify File Info" command (Ctrl-Shift-Q) to add comments (captions) to my JPEG photographs. Unfortunately by default this command preserves the File Modification date & time unchanged.
Most users like to preserve the original timestamp that their camera assigned to the file because it allows them to view the files in chronological order. Photos are different from other files in that respect.
> Today I had to go through a few thousand pictures by hand to identify which ones I had commented
If it should happen again: Turn on the setting that copies image comments into database annotations, re-thumbnail the files, and sort them on annotation (for this, annotations must be made visible in the thumbnail view) to figure out more quickly which files have a comment.
> [..] and then explicitly change their modification times, in order to get them to properly get backed up as should have happened automatically.
Well, ThumbsPlus does offer you the option of updating the timestamp -you just have to remember using it- and it does properly update a file's archive bit when it modifies it (regardless of whether the timestamp is updated), so that should accomodate most backup strategies.
BTW, the Modify File Info dialog that you used deals with oldfashioned image comments from before IPTC and EXIF were introduced:
[*] GIF: Version 89a comment field
[*] JPEG: COM marker field(s)
[*] TIFF: Description tag
[*] PNG: Text fields
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I haven't tried, but I'm not sure if TP also fills the relevant IPTC (caption) and EXIF (user comment) fields, which other programs or other uses of the images may require. If that's an issue, it may be better to edit one of those fields instead, and use the relevant settings in Options | Prefs | Metadata to automatically copy the new contents into the comment field too.