do you mind posting a few examples of the flag and then the checksum? it might help us know how much bits each checksum has, suggesting what kind of checksum it uses, for example if it would've been an MD5 checksum, it would've been 16 byte checksum, if this is true, a MD5 flag should be represented before the MD5 hex code to let the camera lock on the code and confirm it's position bit-wise, explaining well why the flag before the md5 checksum code is an hex 0x80 (dec for 128, which is 16 byte) it might be something different all together, the only thing that will help me to
guess what it is is by you either giving me the hex code or by you giving me the address that reads that and let me pick it out myself, if I happen to have an idea I'd share that
after we do know what kind of checksum it uses, we can have easier time decrypting the image to it's full raw-data format