For FX2 device hex2c.exe converts the hex files to the format which can be used by the C programs. This is useful for including the firmware with the USB driver code to download it to the hw.
Is there any similar utility already available to convert the *.img file or the *.elf file ?
We currently do not have a utility to do this. The elf2img source is available as part of the SDK, in case you're planning to develop your own utility modifying that would be a good idea.