If you need to create floppy disk image on OS X, follow these steps:
Step 1: Open Terminal and type
dd if=/dev/zero bs=1024 count=1440 > floppy.img
This will create an image file called floppy.img.
Step 2: Open Disk Utility application. Go to File -> Open Disk Image and select floppy.img created in step 1.
Step 3: Select floppy.img in Disk Utility, and click on Erase tab.
Step 4: Select MS DOS FAT as a format.
That’s it. Now you have a blank floppy disk image. You’ll now see it mounted on your desktop / Finder and it can now be used as any disk drive on the system. Open it up and copy files into it. Once finished, eject the floppy disk image.