I have had the exclude duplicates item ticked on my picasa imports by default, for the longest time. This helps avoid a lot of duplicates turning up because some photos where left on a card or a phonephoto was uploaded via wifi more than once or via different services, However because I now have my photos flow across several computers and software packages it is surprising just how many duplicates do turn up. So I have also been using a neat little utility program from digital volcano called duplicate cleaner, which is design for all file types but does work very well with media files like photos, video and music. The biggest feature of this cleaner is that it can recognise the same file contents, even if the name is changed. If the file is a jpeg and has been post processed it will be considered as different. Also if the jpeg has been rescaled it will also be considered different. This is fine I probably want to keep these,
During and particularly as I reach the end of the month I move my photos from the collection points (laptop computers) onto a backup drive and it is at this point that it is most useful to run the duplicate cleaner (if you have a lot of files it can take a while …so go get a coffee). After this I then copy the backed up files to the archive drive and make my DVD/CD backup set of the archive (this is my one remaining traditional backup, everything else is now on portable hard drives). I don’t delete the photos on the collection computers until I have finished the backup –> duplicate clean –> Archive cycle. The very end of the month is the right time to do this.