The first thing you have to do is make sure what model you have (the year when your computer has been released) then check on the official apple website to see what is the latest macOS or Mac OS X version available for you computer. I had this problem with a friend computer, it was an old iMac and I'll tell you it is not going to be easy. So basically, the USB drive cannot have any high level formatting, the Windows system should detect the drive as 'not formatted' for this to work, which it will if prepped right with Diskpart. When I tried to inject the image, Transmac told me that the drive was 'write protected'. Note: I use 'Rufus' for all other USB writing and formatting for Windows systems, it's a great app, but I had previously tried to format the drive as GPT using that, as a Fat32 partition. DISKPART> convert gptĭiskPart successfully converted the selected disk to GPT format. DISKPART> cleanĭiskPart succeeded in cleaning the disk. (Find the disk number) DISKPART> select disk x (from result of List Disk)ĭisk x is now the selected disk. Here are the Diskpart commands used to prep the Flash Drive, just to have them here in case my Link does not work: diskpart I've been trying to post this to confirm that it works for some time, I just hope it helps someone else, because it is a very easy solution. Someone had reported that the method for using DISKPART did not work, but I have done this twice and it works remarkably well, and it's the only method I could find to create a Mac-Bootable Flash. I used TransMac on Windows 7 to restore the image file I had to the Flash Drive, it created a bootable Mac image on my flash drive. Dryden's Link, I was able to use the Diskpart command to clean and prep a GPT partition on a flash drive for an OSX Mavericks install image. I was never able to write a Mac installer image to my Flash Drive and have it bootable, unless I did it on a Mac.

I know this question is old but it is still valid.

Create bootable os x usb on windows