How do I extract a picture from iPhoto?

There is indeed a way to extract one or more photographs from the iPhoto library (well, to make copies of the photos, since they'll still be in iPhoto once you're done) but it's a bit more complicated than just dragging and dropping the image onto your Desktop. Rather surprisingly, it doesn't involve the contextual pop-up menu either, if you've tried a Ctrl-click on a photo and been a bit baffled as to why there isn't a "Save As..."

In fact, what you need to do is export the photo or photos from Apple iPhoto to get them out of the application.

To show you, let me pop up a display with a couple of pictures in it:

Select one, then choose "Export..." from the "File" menu:

Easy enough. Once you do that, you'll get a file save dialog window:

Notice here that you can set what graphical file format you'd prefer, whether you want it to be high quality (that is, a big output file) or lower quality, what size, and so on.

Ready? Then click on "Export" and (in a bit of odd user interface design) it then asks where you want to save the photo or photos:

Specify where, and it'll save the photograph or photographs, all ready to upload to another service or do just about anything else you desire.

If you no longer want to have the images in iPhoto, don't forget to Control-click on the images and choose "Move to Trash".