• use disk utility
• drag and drop the img file to the left panel of disk utility
• click convert
• choose cd/dvd master, no encryption
• convert
• done!

For using with Mavericks boot camp the cdr file is fine, you do not have to convert cdr to iso. There are tons of articles on the internet with dd, disk utility and 3rd party software. Mostly, they do NOT work. Though boot camp assistant was asking for iso, the cdr will just work fine.