GRE transform set mode

[MarcusYNT]

Recently i'm very confuse with GRE in transport mode compared to tunnel mode. Which one is true, the GRE IP Header is placed at the front or the GRE IP Header does not use then create new ip header at the front in gre transport mode ?
which mode can be used for gre ?

https://www.researchgate.net/profile/Faycal-Bensalah/publication/316968574/figure/fig7/AS:668797237219335@1536465095770/Protected-GRE-In-the-above-representation-the-GRE-IP-Header-field-corresponds-to-the-IP.ppm

https://i0.wp.com/duconet.com/wp-content/uploads/2017/11/IPSEC_Figure3.png?w=801&ssl=1

[MHM Cisco World]

GRE is always Tunnel, 
the tunnel or transport mode is use for IPSec that can work over GRE tunnel.