Well, there are basically 3 tools.
- start-up disk creator
For most of the cases, the first one would work well – boot from USB drive, then you have a go.
For some other cases, unetbootin could do the job.
And in some rare cases, like mine – yesterday – with Ubuntu Server 14.04.3 LTS x86-64 ISO, only dd works.
Kinda funny experiences.