Yes you can actually create an .iSO image file on your Mac with Disk Utility and a little bit of Terminal magic.
Connect an external drive (or, if you have an older Mac, insert a disc into the CD/DVD drive) to your Mac and launch Disk Utility. This is the device that you will be placing your files on for conversion. A USB Drive is also useful if you can't find an empty Your disk will appear in the left column window.
Now that you’ve selected the source of the disc image, click on File > New > Disk Image from... In the popup window, select Desktop as your destination. Next, make sure to choose DVD/CD Master as the Image Format. Choosing this format ensures the contents of the disk are copied entirely as a .CDR image.
You should keep the image’s name short so that it’s easily reproduced.
If asked, enter your Mac password and hit OK to begin the disk image process. Depending on how large the disc is, the amount of time that’s necessary varies (Which makes USB drives very effecient). You’ll see a progress bar estimating the time until completion.
Once the process finishes, hit “Done,” and check your Desktop for the .CDR image. In its current state, the disk is ready for use on any Mac. To share the file with Windows users, you’ll need to convert it into a recognizable format. To do this, you’ll use your Mac’s Terminal app.
Assuming your .CDR file is on your Mac’s Desktop, open Terminal and type the following and hit the enter key:
Then, enter this line of code to transform the .CDR to .ISO and hit enter:
hdiutil makehybrid -iso -joliet -o [filename].iso [filename].cdr
Substitute both instances of [filename] with the name of your .cdr image. For example, I named my ISO file TEST-IMAGE, so the line of code I used is:
hdiutil makehybrid -iso -joliet -o TEST-IMAGE.iso TEST-IMAGE.cdr
Terminal will create a new hybrid image. This image can be used by both Windows and Mac computers that use ISO 9660 and HFS file systems.