It's no secret that the photo management problem is a huge mess. As new cameras, software, and online storage and sharing services come and go, our collections end up strewn all over the place, often in duplicate. This eats up precious storage space and makes finding that one photo an exercise in frustration.
But, while Apple and/or Dropbox get their act together (I'm not holding my breath), you have to make sense of your photos in your Pictures folder, in your Dropbox Photos folder, in various other Dropbox shared folders, on your Desktop, in your Lightroom, Aperture, and iPhoto collections, and so on. A lot of these might be duplicated because, for example, you were just trying out Lightroom and didn't want to commit to it so you put your pics there but also in Aperture. And by you I mean I.
So, the first step to photo sanity is to get rid of these duplicates. Thankfully, there is an excellent OSX app called Photosweeper made for just this purpose. I used it yesterday to clear 34GB of wasted space on my HDD. (I was too excited to take screenshots of the process, unfortunately!)
There's a lot to love about Photosweeper. First, it is happy to look at all the sources I mentioned above, and compare pics across them. Second, it lets you automatically define a priority for which version of a duplicate photo to save. In my case, I told it to keep iPhoto images first (since these are most likely to have ratings, captions, and so on), then Aperture, then whatever's on my HDD somewhere. If a duplicate was found within iPhoto, it should keep the most recent one.
But, third, what makes Photosweeper truly useful: it won't do a thing without letting you review everything, and it offers a great reviewing interface. It places duplicates side-by-side, marking which photo it will keep and which it will trash. Best of all, this view shows everything you need to make sure you're not deleting a high-res original in favour of the downscaled version you emailed your family: filename, date, resolution, DPI, and file size. Click on each file and the full path (even within an iPhoto or Aperture library) becomes visible. This is in stark contrast to iPhoto's lame "hey, this is a duplicate file" dialog that shows you two downscaled versions of the images with no further information.
Once you bite the bullet, it does exactly the right thing with every duplicate: iPhoto duplicates get put in the iPhoto Trash, Lightroom duplicates get marked "Rejected" and put in a special "Trash (Photosweeper)" collection, and filesystem duplicates get moved to the OSX Trash. Lesser software might have moved all the iPhoto files to the OSX Trash, leaving the iPhoto library broken.
In all, I was really impressed with Photosweeper. 34GB is nothing to sniff at and getting rid of those duplicates is the first step to consolidating all my files. It does this in a very accountable, safe way. At no point did I get that sinking feeling of "there is no undo."
Finally, I should mention that Photosweeper also has a "photo similarity" mode that finds not only duplicates, but very similar series of photos. This is really good for when you snapped 15 pics of the same thing so that one might turn out ok. But I'm too much of a digital hoarder to take that step!
Photosweeper currently sells for $10 on the Mac App Store.