Wut. The parking spaces are viewable by my apartment window.

Point a camera at the spots when unoccupied.Specify the spots exact coordinates to the camera. Set color as baseline. If the color changes by 50% or more, they are occupied. Send alert when all occupied, or when not all occupied.

Now, learn to code it.

Well I've got the raspberry pi, mjpeg, a camera that works. Just need to make the logic work. Here is what I'm stuck on. http://i.imgur.com/pIy3QNt.jpg

Or just remotely send yourself a photo of your parking lot.

You could also zoom in so you would be looking at a car if it is parked there, and then upload the image to the microsoft caption bot service. It's pretty good at recognizing cars already, and you can just search the result for the word "car"

Couldn't you just get a decent security camera and uh, well... look?

The challenge, of course, is snow.

Also: clouds, nighttime, people walking across the lot, and any other color changes that aren't related to other vehicles being parked in the spots.

Plug in a webcam, and upload a photo to a server every minute or so. Or put the Pi online.

Humans are still better at parking spot recognition than $35 hardware.

Of course you'll need a camera with a time machine so you know the spot will be free when you arrive, and not just when you set out.

IFTTT api to create geo fence on my route home to poll the Pi "are there spaces left?" with an email or response yes or no with a photo at the current time.