http://www.dvdtoiso.com/
Remark:
1. This software is a freeware, free for personal and non-commercial use.
2. Software supports both 32-bit and 64-bit Windows OS (.NET Framework required).
3. The output ISO file format is ISO 9660 (CDFS, a standard file system for CD-ROMs).
Here they are other blog's useful articles too:
Program - How to backup exact copies of USB flash drives
http://www.alessandromazzanti.com/2014/10/program-how-to-back-up-exact-copies-of.html
Program - How to backup exact copies of USB flash drives
http://www.alessandromazzanti.com/2014/04/cd-live-iso-to-usb-bootable-only.html