OS X :: MacBook Running Out Of Space On Startup When Editing Photos Stored On External

I had a bunch of photos stored on my digital camera that I wanted to upload onto my computer. Only I had a little under 2 GB of free space on my startup disk, which was not going to be enough, so I uploaded them to an iPhoto library I created on my external hard drive. The free space that Finder recognized on my startup disk dropped to around 1 GB during the time it took to upload the 1300 or so photos onto the external drive, which was slightly surprising in that it's never taken so short a time, but I restarted my computer and it went back to recognizing the right amount of free space, like it always has after restarting. Everything was working just as I expected.

However, when I edited about 1000 of those photos in iPhoto, somehow this ate up almost all of the hard drive space on my LAPTOP, not my external drive, and restarting my computer did absolutely no good. I am literally running on 13 MB of free space as I type this.

The photos are definitely in my external iPhoto library, not on my startup disk. I searched my startup for "IMG" (my camera names photos "img_###" to see if for some reason iPhoto was copying the pictures I edited to my laptop, but none of these new pictures came up. I even went into the files I'd accessed yesterday (it's past midnight here) to see if I could figure it out, but all the photos I clicked on were on the external disk. That iPhoto is copying the pictures I edit somewhere is the only possible solution I can think of. But whatever it is that is taking up all my free space, I can't find it.

Meanwhile, and similarly inexplicably, the copy of Cocktail I have downloaded is telling me that I am currently using only 71% of my available disk space, which uh, has basically never been true ... Cocktail has always told me that I'm using something depressing (yet accurate) like 93% of my available disk space.