Trackx,
I do not know if you found the answers you were looking for in another forum, however, I believe the answers to your two questions are as follows:
1) I really like dupeGuru Standard edition for finding ALL of my duplicate files, including photos, on my Mac.
In addition to the Standard edition, there is one specific for finding duplicate pictures (PE) and another specifically for finding duplicate Music files. I've had the best luck with the Standard edition, although it could be interesting to use a feature in the Picture edition that lets you scan for duplicates based on EXIF data.
All three editions are free to download and use (the developer says he doesn't want any money), are opensource and the dupeGuru website has lots of information on how they work and all the ways you can customize your scans. It's actually pretty straightforward though if you just want to jump in and start finding duplicates. Another thing I like is that it doesn't AUTOMATICALLY do anything with the duplicates it finds and lets me check each one out before I decide if I want to delete it or not.
Just do an internet search for 'dupeguru' and I'm sure you'll find it. It's WAY better than trying to go through and find each copy of a picture manually in every possible place on your computer. It even found duplicates that I didn't know existed in places I didn't know they were taking up space (I think because of something iPhoto was doing that I haven't exactly figured out yet. I don't like iPhoto and only use it occasionally for its ability to rotate photos a specific number of degrees.).
2) When sorting photos by date the Date Created can mean different things; it can mean EITHER the date it was uploaded to my computer OR the date the photo was taken and I think it depends on the input source (what you used to take the picture).
To figure it out, do this:
Once you get the photos on to your Mac, check the EXIF data by opening the image and getting the info on it (Apple "i"). It gives additional date time information on the picture such as "Date Time Digitized" and "Date Time Original".
For example, I used bluetooth file transfer to get photos off a non "smart phone" (a Samsung flip phone) and the Date Created is the date I transferred it on to my Mac. However, I notice that if I took a photo with my iPhone and got it on my Mac with Image Capture, the Date Created value is the date that it was taken, not the date that I put it on my Mac. The date I uploaded it to my Mac becomes the value under "Date Modified" (at least until I change / modify the file, that is).
From all that I figure if the Date Time Original in the photo's EXIF data matches "Date Created" in File Manager, then the original file is already a digital image and the Date Created field gets populated by the information found in the file's EXIF data.
If however you notice that the Date Time Original timestamp in the photo's EXIF data is different from Date Created in File Manager, then the Date Created is most likely the date that it was uploaded to your computer, not the date that it was actually taken.
I hope this helps. If you found out any additional information that supports or contradicts what I figured out on my own from just poking around in Preview and File Manager, I'd love to hear it.
Thanks!