What software can find close duplicates from 2TB worth of pictures?
The best that I could find and have used is Duplicate Annihilator, which works with iPhoto, and is upgraded for 10.8.  You can download and do a run and hopefully get rid and clean your folders the first time through.  For what you need you might need a few passes to get the obvious dups, then find the harder to get ones.

http://www.brattoo.com/propaganda/

I am not exactly sure it will find your #2 and #3 right out of the gate, but since photos are marked with unique timestamps and other meta data, it should find them even if rotated.  The similar part is a bit harder as the criteria for similar could be many things.  Run through a few times first checking my filename, then maybe dimensions, creation date, etc.

KEY FEATURES


Detects duplicates
Detects imported thumbnails
Detects missing images
Easily find and annihilate duplicates created internally by iPhoto or during import.
Compare images using different algorithms to detect and understand differences.
Detect duplicates using effective algorithms using electronic checksums like MD5.
Detect duplicates by using file specific meta data such as filename, dimensions, filesize, Exif creation date or date of creation.
Delete duplicates upon detection or mark them with a keyword to make them easily found using iPhoto features like search or smart folders.
Only uses standard Apple features and API's. No hacking nor tampering with iPhoto system files.
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