How do I find all of my photos that are NOT on Flickr?

Download all your photos and check for duplicates. Delete both copies of all duplicates. Upload whatever's remaining. Don't just delete your entire flickr library unless you don't care at all about comments, view counts, sets you've created, etc, because you'll lose all that along with the photos.

https://www.gpsoft.com.au/help/opus9/default.htm?turl=WordDocuments%2Fflickrsynchronization.htm that may match the photos up.

I don't want to delete from either source since there are existing tags and organization. Directory Opus does look like it would do the job, but I only want to do this once and that costs close to $50 US. I'd be willing to pay $20 but not $50.

Directory Opus does have a 60 day fully functioning trial.

I did find a simpler way to get a list of all the pictures I have uploaded to Flickr: They have an API and you can use it directly on the API Documentation pages. I made sure all of my photos were in a set and used http://www.flickr.com/services/api/explore/flickr.photosets.getList to get a list of my sets. Then I used http://www.flickr.com/services/api/explore/flickr.photosets.getPhotos to get a list of the pictures in each set. This gave me a list of all the files in json and I used Excel to parse that into just the Flickr ID and the Title. I had changed some titles, but most of them are the same as the file name. I have some duplicate file names, but they are easy to figure out between the Flickr set name and my folder name. I kept looking because I had tried some of the sync services and I got odd errors some of the time.