Convert bootable USB to ISO file

To create an image from a drive

sudo dd if=/dev/sdx of=/path/to/new.iso

Alternatively, to create a USB drive from an image

sudo dd if=/path/to/iso of=/dev/sdx

Replace /dev/sdx with your USB drive, e.g. /dev/sdc.

WARNING: It is imperative that you make certain you are using the correct drive. If you don't use the correct drive, you could lose your data. To check your currently mounted drives, use the command lsblk.

Note: Copying large files (1 GB or higher) can take a long time, be patient.

Another option is to use gnome-disks.

You can start if from a terminal with gnome-disks or look for the application Disks in the Dash.

Once the USB stick is mounted, select it and use the more actions icon to choose Create Image.

Disks is a GUI for the same command.

"USB Image Tool" is a freeware for Windows which can create images of your BOOTABLE USB flash drives and also allows you to restore them later. This free tool can be used to create backup images of almost all types of BOOTABLE USB devices such as flash drives, card readers, digicams, cell phones and mobile music players.

Its a portable tool so you don't need to install it. Just download and run the program. Using the program is very easy. You can create the backup or restore the backup in a few clicks.

It can be used in Windows XP, Vista, Windows 7 and Windows 8. Both 32-bit and 64-bit editions are supported.

You can download it using following link: http://www.alexpage.de/usb-image-tool/download/