Many Mac users have noticed that the iSight camera takes mirrored photos with Photo Booth. Fortunately there is a very easy fix to this. It is not the camera that is broken. Apple just made a bad choice on their Photo Booth software. If you open up the video capture window in iMovie, you will notice the image is correct.
To fix Photo Booth, just go to Edit>Autoflip New Photos. The preview window will still show the mirrored version, but once you take the picture the saved version will be correct. This does not fix the problem for taking videos, though; just use iMovie or another webcam capturing application.