A blockchain in this case would just be a timestamping service, to prove the minimum time that elapsed since the image existed. That’s only useful if the time to create a fake is significantly more than the resolution of the chain - 10 minutes for bitcoin, 15 seconds for ethereum.

But that I only makes sense if you know ahead of time that the information will be valuable, and it only proves the age if there is sufficient hash power on the network, so a “private” blockchain would not be viable.