Official installers are typically provided as .dmg or .pkg files, while community archives often provide .iso or .bin for virtual machines and bootable USBs.
Are you installing this on or a virtual machine ? Official installers are typically provided as
: You can Download OS X El Capitan as a disk image file ( .dmg ). Official installers are typically provided as
: The standard Mac disk image. Best for creating bootable USB drives on a Mac. Official installers are typically provided as