Specific to BIOS images, `binwalk` is probably a better choice than `strings.` There's often data in LZMA streams or otherwise compressed, and chances are you're gonna binwalk your image at some point if you want to modify it.

Also, specific to Intel powered motherboards newer than a certain generation, the image should show as an "Intel PCH File Descriptor" or something if you run `file` against it. Don't use this as an integrity check though, `file` is just looking at an Intel-specific header at the beginning of the ROM file.