First need a pen with FAT16 (this is not an accurate information)
FAT32 also works (without LBA ?!?) , something the dificult is make the pen usb, boot ...

fdisk -l /dev/sdb

Disk /dev/sdb: 1,9 GiB, 1992294400 bytes, 3891200 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x844f3a44

Device     Boot Start     End Sectors  Size Id Type
/dev/sdb1  *        1 3891199 3891199  1,9G  6 FAT16

with gparted (fat16 + flag bootable)

Than we can put boot.iso on a usb stick (now also copied and ranamed as Network
Installers),
for example:
https://alt.fedoraproject.org/
wget https://download.fedoraproject.org/pub/fedora/linux/releases/25/Workstation/x86_64/iso/Fedora-Workstation-netinst-x86_64-25-1.3.iso

As root usb must be formated or else format usb with:
# mkfs.vfat /dev/sdb1.

# /usr/bin/livecd-iso-to-disk --reset-mbr Fedora-Workstation-netinst-x86_64-25-1.3.iso /dev/sdb1

(just need add --reset-mbr if before the pen usb isn't bootable)

and check if boots:
qemu-system-x86_64 -drive format=raw,file=/dev/sdb


Info deprecated:
Answer the question, Where is diskboot.img
( http://www.redhat.com/archives/rhl-beta-list/2008-April/msg01563.html )
boot.iso is the replacement, and we can boot on USB like explain above.