I) Use ImageMagick to perform the batch processing from PNG to JPG while preserving the timestamp:

mogrify -verbose -define preserve-timestamp=true -format jpg -quality 60% -path ./output/ ./input/*.png

• preserve-timestamp correctly preserves the creation and modification timestamps in the filesystems.
• But in the EXIF header timestamps are NOT created!
  • As I read in a forum post from 10/2018 writing EXIF metadata seems not to be in the scope of ImageMagick.
  • Hence the use of another tool:

II) Use ExifTool to copy the creation date in the filesystem to the creation and modification date in the filesystem and into the EXIF header of the file.

exiftool "-alldates<filecreatedate" ./output/

III) As of exiftool 12.26 on macOS 11.4 Big Sur (ca. 08/2021) the above results in a bug which I reported like this:

• ✅ The EXIF timestamp is written correctly
• ❌ But the creation and modification timestamps in the filesystem get set to now.
• So one more processing task:
  • In another tool which can copy timestamps between EXIF and the filesystem such as A Better Finder Attributes:
    • Copy EXIF timestamp to creation timestamp.
    • Copy creation to modification timestamp.
    • (Or in one pass if the software supports it.)

I) Use ImageMagick to perform the batch processing from PNG to JPG while preserving the timestamp:

mogrify -verbose -define preserve-timestamp=true -format jpg -quality 60% -path ./output/ ./input/*.png

• preserve-timestamp correctly preserves the creation and modification timestamps in the filesystems.
• But in the EXIF header timestamps are NOT created!
• As I read in a forum post from 10/2018 writing EXIF metadata seems not to be in the scope of ImageMagick.
• Hence the use of another tool:

II) Use ExifTool to copy the creation date in the filesystem to the creation and modification date in the filesystem and into the EXIF header of the file.

exiftool "-alldates<filecreatedate" -overwrite_original_in_place -P ./output/

• overwrite_original_in_place causes that this remains the same file, hence the creation date stays as-is.
• -P preserves the modification timestamp of the original file which is overwritten in place.
• And the EXIF timestamp is also updated because it's included in -alldates.