I've been struggling with the same problem but this works for me:
- convert the .dmg image with power iso to iso
- put the iso on a usb stick (drag it into your mac hard drive and mount it)
- format your usb stick with the disk utility tool. (Make sure the usb is partitioned as mac bootable then use use the image recovery and put your mounted OS X iso into the source and your usb as the location.)
- restart your computer while holding down the option key
