Easy
# dd bs=4M if=/path/to/file.iso of=/dev/sdX status=progress oflag=sync
Under Linux, you can create an ISO image from a folder using a command line argument with the mkisofs tools. The following example creates an ISO image suitable to be used under Windows:
# mkisofs -J -l -R -V "Label CD" -iso-level 4 -o output.iso input_directory