Updated 2/6 after latest Lion update that ruined everything.
I take screenshots all the time, and I hate the default black camera that Mac OS X has when you do selection captures. I figured it would be easy as hell to replace it: just find that icon, then switch it with the one I want. So while Jimmy made the world’s best grilled cheese sandwiches last night, that’s exactly what I did.
The first task was finding original camera image. I actually lucked out by assuming it was in a folder of cursors, since that’s what it technically is. I searched my Mac for “cursor” and it fortunately popped up pretty quickly (my machine is running Mac OS X Lion 10.7.2, by the way). You can do the same, or go to the patch of the folder it resides in. See the following screenshot to see what I mean – it’s quite a mouthful:

Edit 2/6/2012: Of course, the day after I published this, a new Lion update was released that not only changed the default cursor to an even UGLIER camera, but it also changed the format for the cursor from .png to .pdf. W.T.F. I’ve updated the following instructions accordingly. If you refused the update, you’ll see the cursor.png instead of cursor.pdf.
Once you’re in the folder that contains cursor.pdf, you want to open that image in Adobe Illustrator, or any graphics editor that will preserve the original cursor.pdf’s state, to add a layer for your new camera graphic, then delete the original layer. This way your new cursor is in the same mode and format as the original cursor. Bill Brown’s Camera Collection is hands-down the best place to go if you want to find 8-bit-style camera icons. Since I love my Diana+, I grabbed that illustration to be my new screenshot cursor.
Save the new cursor you made to your Desktop, as the cursor.pdf’s folder is not editable without authorization. Name it “cursor.pdf” and drag it into the cursor.pdf folder. The OS will most likely bark at you and make you log in.

I renamed the original cursor to “cursor-original.pdf” just in case I wanted to revert to it in the future. Once you’ve replaced “cursor.pdf” with your snazzy new icon, restart your machine to watch it take effect. No more boring camera cursor!

How I ever slept at night before I did this, I’ll never understand.