Recover photos from thumbnails in Photos app

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.

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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. Free updates! Available in English, German, French, Italian and Swedish.

When you choose to export from Photo (File>Export), choose TIFF, 16-bit and you should get a full quality, uncompressed, but edited image out of Photo. This is what the settings in the export dialog box will look like:

The reason you haven't found the folder with the edits are that image editing programs such as Photo or Adobe Lightroom perform non-destructive edits as an instruction set that sits in a database that references the original image. Basically your edits just create a recipe that the software then can use to create an output file. If you choose to print, it will give the instructions on how to render the edited image to the printer. The only time you will get an edited file is if you export to a file format such as JPEG or TIFF.

TIFF gives you an uncompressed file, and by choosing 16 bits, the software is actually interpolating to add pixels to your photos as most digital camera sensors produce a 12 or 14 bit image. There isn't much of a point for more, as the human eye has a hard time distinguishing the available gradations of a 16-bit dynamic range.

JPEG is a Lossy compression format, but for even a 5K iMac, if you go for the highest quality, largest file size, you will likely not be able to see a difference between the TIFF and the JPEG version of the file, and you will have a file that is probably 80% smaller, depending on the subject matter.

You also have the option of exporting the Unedited originals (Raw files) using this option as well. There is an option to export IPTC data as an XMP sidecar file.