correct picture taken info

What I want is for the picture-taken date to be the operative and/or default date in Photos, iPhoto, Flickr, etc. The date loaded or modified is not significant for me and is just plain confusing. Is there a method for making this happen?

No. Photos does not support this.

While in Photos you should always be seeing the capture date displayed. As soon as you export a file to folder in the Finder and the photo will show the file attributes in the Finder, not the photo attributes. You would need third party software to replace the file creation date by the capture date, for example A Better Finder. When you upgrade to Mojave in the fall, you may be able to see more metadata for a photo in the Finder, this is shown in Apple's preview of Mojave, see: https://www.apple.com/macos/mojave-preview/

If the photo has been taken with a camera, the camera will embed an EXIF tag with the original capture time. This tag will be shown in the Info panel in Photos (as Marco Kobas explained) and most photo editing programs can read it and show it. The Finder on the other hands treating a photo as a file and will show you the date, when the file has been created. when you save an edited version of a photo to the desktop, a new file will be created, when Photos renders the adjustments, so the Finder is showing a different date. But you can open the Image file in Preview to see the actual capture date in the EXIF tag. You can display the EXIF tags in Preview with the command "Tools: Show Inspector".

In iPhoto and Photos the capture date *is* the "operative" date. You have to work really hard and possibly muck around in the library to even see the file date.

The only time it is an issue is when you are exporting.

If you open an exported photo in Preview and invoke the Inspector (menu Tools -> Show Inspector) you get in the Exif tab the date when the picture has been taken.