I have seen other questions and answers that say given a new phone shipped from a retailer, it is only possible to verify the integrity of the firmware by comparing checksums.

However, I'm not sure how to get the checksum of the currently running firmware on my device. Is this even possible? I may have misinterpreted the other advice as comparing checksums for downloaded images, but I am specifically looking to check the firmware that came loaded on the phone against a valid source before re-imaging it if that's what I decide to do. Hoping for generic advice, but manufacturer is LG if it matters. Please suggest tools and process.

Final note: The phone has been used since it was received, so if there is a way to capture the pre-loaded firmware, I want to make sure it is not affected by any software/user option changes that would be made after the device setup was complete. I'm guessing I want to get a checksum of the current software version, so not sure if I have to make an image first and if that firmware image that is created would be static.