On https://dortania.github.io/OpenCore-Install-Guide/installer-guide/mac-install-dmg.html, it states

The below installers were pulled from genuine Mac restore disks with their SMBIOS lock removed, contents of OS X itself have not been modified in any way.

This is not true for Leopard. Leopard's disk image does have an SMBIOS lock, when attempting to install with an iMac7,1 SMBIOS, I get the error "Mac OS X cannot be installed on this computer". When switching to MacBookPro5,3, Mac OS X can be installed without issue. iMac7,1 supports 10.5.7 so that means the SMBIOS lock is still present. Either the DMG should be modified to have the SMBIOS lock properly removed or it should be noted in the guide that you need a MacBookPro5,3 SMBIOS to install Leopard.