As you want to create a LiveUSB you need a
.ISO image to make it. The Mac image is a
.dmg file, so you must to convert this file into
.ISO, and then install it.
This software will convert the
.dmg image into a
Open a terminal and enter this command:
sudo apt-get install dmg2img
Now you have the converter software.
dmg2img you will creat an
.IMG file, and this file will have the same code that an
.ISO file, so you will fix the extension.
In the terminal you have to enter the following commands:
dmg2img OriginalFile.dmg #Replace with your file name and it will create the IMG file
mv OriginalFile.img FinalFile.iso #NOTE that the extension of the first file is .IMG!
Now you already have the
.ISO image, with which you will make the LiveUSB. Actually is an answer where this procedure is explained very well, so see that document.