A small utility I use with binaries built from iBoot src.

$ Usage : ibooter [OPTIONS]
 -i, --img3 [file] <tag>       create IMG3
 -l, --load [IMG3]             load IMG3 file
 -k, --kickstart [file] <tag>  create and load img3
 -m, --mode                    device mode
 -s, --shell                   start recovery shell
 -d, --diags                   start device in diagnostic mode
 -h, --help                    print help

• libimobiledevice
• libreadline
• libusb

Run make

1. Build iBoot source code
2. Grab binary file (eg iBEC.bin)
3. Run ibooter [file] <tag> where file is iBEC.bin and tag is ibec
4. example : ./ibooter -i iBEC.bin ibec

Once you have built the IMG3 file, and your device is in kDFU mode run :
./ibooter -l iBEC.bin.img3

As most of the code is from other repositories, see licenses at the top of C files in src.
If I broke licenses feel free to open a issue so I can fix it.