Can we copy the virtual image (machine) hosted on one ESX box to another ESX box ?
Yes you can do that.
If the ESX hosts are part of a VC cluster you can cold migrate the VM or vMotion the VM.
If you don't have VC you can export the VMDK (using vmkfstools), transfer the exported VMDK (and maybe the VMX file too) to the other host.
Then import the VMDK (again using vmkfstools) and create a new VM or point the VI client to the copied VMX file.
If you copy the VMX file make sure to check it for different paths.
Another option is to use VMware Converter.
In short: Yes.
If you are using Virtual Center do a Cold Migrate.
If you are from console you should use vmkfstools to export the .vmdk file.