The easiest way to remove background from photo on a Mac. : )
1. Your Image.
2. “Select” -> Choose “Instant Alpha”
3. Just drag on the place that you want to cut. And then press “delete” button.
4. After That, Save as PNG, PDF, TIFF or GIF file. Don’t forget to check “Alpha”
5. Done! : )
Note: This option also can use via Keynote from iWork.