This video demonstrate the creation of bootable USB from ISO image file. The creation of other bootable USB's is similar to this except you have to download the particular ISO file. The links for
Windows 7 ISO files are here
Download link for Windows 7 ISO Image from below: You can download both 32 and 64 bit versions from here
http://getintopc.com/softwares/operating-systems/windows-7-ultimate-download-official-iso-32-64-bit-dvd/
Try these for direct links in case the above link does not work
32bit:
http://85.25.103.173/Getintopc.com/Win_7_32Bit.iso?md5=IELffz3z0UkzZoqUh_YnFw&expires=1453772172
64 bit:
http://188.138.1.16/Getintopc.com/Win_7_64Bit.iso?md5=iXCd2XOOc5UXzxHA-t5ruA&expires=1453772174


Download YUMI from here:
http://bc.vc/mBAysx

If above link doesn't work, then try this link:
http://bc.vc/dzDmip